Skin Lesions: Types, Causes, Diagnosis, Treatment, and Pictures

An abnormal area on the skin that is structurally different from the surrounding skin is referred to as a skin lesion. These lesions are incredibly common and can appear suddenly or develop over time, ranging from a minor cosmetic blemish to an indicator of a more serious underlying health issue. Understanding the different types of lesions, their potential causes, the diagnostic procedures, and the available treatment options is fundamental to effective skin health management. Skin lesions are categorized based on their appearance, depth, and whether they are primary (arising from previously normal skin) or secondary (resulting from changes to a primary lesion, such as scratching or healing). This comprehensive guide explores these aspects in detail, providing an educational resource for identifying, understanding, and addressing common skin abnormalities.

Types of Skin Lesions: Primary and Secondary Classification

Dermatologists classify skin lesions into two main categories: primary lesions and secondary lesions. Primary lesions are the initial, spontaneous manifestations of a disease process. Secondary lesions develop from a primary lesion due to external factors, such as scratching, infection, or the natural progression of the underlying skin condition. A precise description of a lesion’s characteristics is the first critical step in diagnosis.

Primary Skin Lesions

Primary lesions are those that have not been modified by trauma, scratching, or natural involution (healing). They represent the purest form of the underlying skin condition.

Macule and Patch:
A macule is a flat, non-palpable change in skin color that is less than 1 centimeter (cm) in diameter. Examples include freckles or flat moles. A patch is a flat, non-palpable discoloration that is larger than 1 cm, such as in vitiligo or a port-wine stain. Both macules and patches are distinguished solely by their size and their lack of elevation or depression.These lesions often represent changes in pigmentation or vascularity without any alteration to the texture or thickness of the skin. They are typically diagnosed through visual inspection and sometimes dermoscopy.
Papule and Plaque:
A papule is a small, solid, raised lesion that is less than 1 cm in diameter. They can be found in conditions like acne, warts, and some rashes. A plaque is a large, raised, flat-topped lesion that is greater than 1 cm in diameter, often formed by the coalescence of multiple papules. Psoriasis is the classic example of a plaque-forming skin disease.These lesions are palpable, meaning they can be felt when running a finger over the skin, which helps distinguish them from flat macules and patches. Their texture and scale (or lack thereof) are important diagnostic features.
Nodule and Tumor:
A nodule is a solid, elevated lesion that is usually larger than a papule (typically >1 cm) and extends deeper into the dermis or subcutaneous tissue. They feel like a firm, distinct mass beneath the skin surface. A tumor is a large nodule (often >2 cm) that suggests deep extension and can be benign or malignant. Examples include lipomas or deeper cysts.The depth and consistency of a nodule or tumor are assessed by palpation. Their presence often warrants a deeper investigation, such as ultrasound or biopsy, due to their potential complexity.
Vesicle and Bulla:
A vesicle is a small, elevated, fluid-filled sac (blister) less than 1 cm in diameter. Common examples include those seen in herpes simplex, herpes zoster (shingles), or acute allergic contact dermatitis. A bulla is a large vesicle, greater than 1 cm in diameter, such as those found in bullous pemphigoid or severe burns.The fluid content can be clear, cloudy, or hemorrhagic, providing clues to the underlying cause. The tension and thickness of the blister roof are also key characteristics noted during diagnosis.
Pustule:
A pustule is a small, elevated lesion filled with pus—a cloudy or yellowish fluid composed of inflammatory cells. They are a hallmark of inflammatory conditions such as acne, folliculitis (inflammation of hair follicles), and some bacterial skin infections.Although often associated with infection, not all pustules are infectious. They can be sterile, as is often the case in some forms of psoriasis or drug reactions, requiring microscopic analysis for definitive identification.
Wheal (Hives or Urticaria):
A wheal is a raised, localized area of edema (swelling) in the skin that is transient, meaning it appears rapidly and often resolves within 24 hours. They are typically pale pink or red and can vary widely in size. Wheals are the characteristic lesion of hives (urticaria).Wheals are caused by the release of histamine, which causes local vasodilation and leakage of fluid into the superficial dermis. Their transient nature is a critical diagnostic feature.

Secondary Skin Lesions

Secondary lesions are modifications of primary lesions that occur during the evolutionary process of the skin disease or due to outside interference, such as scratching or topical treatment.

Scale: Scale is an excess of dead keratinized cells that appear as flakes or plates on the skin surface. They result from abnormal keratinization and exfoliation. Conditions like psoriasis, which presents with thick, silvery scales, and seborrheic dermatitis, with yellowish, greasy scales, are defined by this feature.The color, size, and adherence of the scale are important descriptors. For instance, the fine, white scale of tinea versicolor differs greatly from the thick, adherent scale of chronic plaque psoriasis.
Crust: A crust, also known as a scab, is dried serum, blood, or pus mixed with epithelial and sometimes bacterial debris. It forms over a damaged epidermis (e.g., following a burst vesicle or pustule) as the lesion heals. Impetigo often presents with characteristic honey-colored crusts.Crusts protect the healing tissue beneath, but they can also harbor bacteria. Careful removal of a crust may reveal an underlying erosion or ulcer.
Erosion: An erosion is a superficial loss of the epidermis (the top layer of skin) that does not extend into the dermis. Since the wound is superficial, erosions heal without scarring. They often result from the rupture of vesicles or bullae or from scratching.They present as moist, depressed areas. Understanding the initial lesion that led to the erosion is key to determining the underlying diagnosis.
Ulcer: An ulcer is a deeper loss of tissue that extends through the epidermis and into the dermis or even deeper subcutaneous tissue. Because the loss of tissue is extensive, ulcers always heal with scar formation. Common causes include venous insufficiency, arterial disease, pressure, or trauma.The size, depth, margin, base, and surrounding tissue of an ulcer are all meticulously examined during a physical assessment to determine the cause and guide treatment.
Fissure: A fissure is a linear crack or break in the epidermis, often extending into the dermis. Fissures typically occur when the skin is very dry and thickened (lichenified), such as on the palms, soles, or corners of the mouth (cheilitis).They are often painful and can serve as portals of entry for bacteria. They are particularly common in severe, chronic eczema or fungal infections of the feet.
Lichenification: This is a thickening of the epidermis with exaggeration of normal skin lines, resembling tree bark. It is a secondary lesion that results from chronic scratching or rubbing (pruritus). This thickening is a defense mechanism of the skin against persistent irritation.Lichenification is often seen in chronic atopic dermatitis (eczema) or chronic contact dermatitis, indicating a long-standing pattern of scratching and irritation in the affected area.

Causes of Skin Lesions: A Comprehensive Overview

The underlying causes of skin lesions are vast and varied, encompassing everything from minor trauma and infectious agents to complex systemic diseases and malignant transformation. Grouping the causes into broad categories helps to logically organize the differential diagnosis.

Infectious Causes

Infections are a major and common cause of many types of skin lesions, caused by bacteria, viruses, fungi, or parasites.

Viral Infections: Viruses can cause a wide array of skin lesions, from single growths to widespread rashes. For example, the varicella-zoster virus causes the highly characteristic vesicular rash of chickenpox and shingles. The human papillomavirus (HPV) causes warts, which are nodular, verrucous lesions.Diagnosis often relies on the characteristic appearance of the lesions and, in some cases, laboratory confirmation (e.g., a Tzanck smear or PCR test for herpes viruses).
Bacterial Infections: Bacteria are responsible for common skin infections like impetigo, which presents with pustules and honey-colored crusts, and cellulitis, which manifests as a large, painful, erythematous (red) patch or plaque. Folliculitis, an inflammation of the hair follicle, often presents as small pustules.These infections frequently require systemic or topical antibiotics. A culture of the pus or fluid may be necessary to identify the specific bacterium and its antibiotic sensitivities.
Fungal (Mycotic) Infections: Fungi are responsible for infections commonly referred to as tinea (ringworm). Tinea corporis (body ringworm) typically presents as an annular (ring-shaped) scaly patch with central clearing. Candidiasis (yeast infection) can cause erythematous patches in skin folds.Fungal infections are usually diagnosed by scraping the scale and viewing it under a microscope using a potassium hydroxide (KOH) preparation, revealing the hyphae (filaments) of the fungus.
Parasitic Infestations: Lesions caused by parasites include the linear burrows of scabies (a mite infestation) or the bites and secondary lesions (like lichenification) resulting from insect bites, such as those from mosquitoes, fleas, or ticks.These often present with intense itching (pruritus) that is worse at night. Scabies is confirmed by finding a mite, eggs, or fecal matter (scybala) in a skin scraping.

Inflammatory and Immunological Causes

Many skin lesions are the outward manifestation of an immune reaction, where the body’s defense system mistakenly attacks its own cells or overreacts to an external trigger.

Eczema (Dermatitis): This term covers a group of conditions characterized by inflammation. Atopic dermatitis (a type of eczema) presents as red, itchy, sometimes weeping patches or plaques, which, when chronic, can lead to lichenification. Contact dermatitis (allergic or irritant) presents as an erythematous, sometimes vesicular, rash localized to the area of contact with the offending substance.Management involves identifying and avoiding triggers, as well as topical corticosteroids or calcineurin inhibitors to control inflammation and intense moisturization to repair the skin barrier.
Psoriasis: An autoimmune condition characterized by a rapid buildup of skin cells, resulting in thick, silvery-white scales on red plaques. Common sites include the elbows, knees, scalp, and lower back.Psoriasis is a chronic condition treated with a stepwise approach, including topical agents, phototherapy (light treatment), and systemic or biologic therapies for more severe cases.
Urticaria (Hives): An allergic reaction resulting in wheals (hives) that can be acute or chronic. The reaction is typically triggered by foods, medications, insect stings, or environmental factors.Treatment is primarily aimed at symptom relief and suppressing the histamine release, commonly achieved with oral antihistamines. Identifying and removing the underlying trigger is essential for long-term management.
Drug Eruptions: Various medications can cause skin lesions, ranging from a simple morbilliform (measles-like) rash (a maculopapular eruption) to severe, life-threatening conditions like Stevens-Johnson syndrome/Toxic Epidermal Necrolysis (SJS/TEN).Diagnosis is often based on the timing of the drug initiation relative to the rash onset. Immediate withdrawal of the causative drug is the most critical intervention, followed by supportive care.
Autoimmune Diseases: Systemic diseases such as Lupus Erythematosus can cause distinct skin lesions. Discoid Lupus presents with scaly, erythematous patches, often leading to scarring, most commonly on the face, scalp, and ears.These conditions require systemic treatment, typically with immunosuppressants or antimalarial drugs, to manage both the skin and internal organ involvement.

Neoplastic (Growth-Related) Causes

Neoplasms refer to new, abnormal growths that can be benign (non-cancerous) or malignant (cancerous).

Benign Neoplasms: These are common, non-harmful growths. Examples include Seborrheic Keratoses (tan, brown, or black “stuck-on” plaques), Dermatofibromas (firm, button-like nodules, often resulting from trauma), and Cherry Angiomas (small, bright red papules composed of blood vessels).Generally, these lesions require no treatment unless they become irritated, symptomatic, or if there is cosmetic concern. They are often diagnosed by their characteristic visual features and dermoscopy.
Pre-Malignant Lesions: These lesions have the potential to progress to cancer if left untreated. The most common example is Actinic Keratosis (AK), which presents as a rough, scaly, crusty patch or papule, usually on sun-exposed areas. AKs can transform into Squamous Cell Carcinoma.Treatment for AKs is preventative and involves cryotherapy (freezing), topical chemotherapy creams, or photodynamic therapy to destroy the abnormal cells before they become malignant.
Malignant Skin Cancers: The three most common types of skin cancer are Basal Cell Carcinoma (BCC), Squamous Cell Carcinoma (SCC), and Melanoma. BCC often appears as a pearly, translucent papule with rolled borders. SCC can look like a firm, red nodule or a scaly patch that may ulcerate. Melanoma is the most dangerous, often presenting as an asymmetrical, irregularly bordered, multi-colored lesion larger than a pencil eraser, evolving over time.Early detection and prompt surgical removal are critical for all skin cancers, especially melanoma. Treatment may also include radiation, chemotherapy, or targeted molecular therapies, depending on the stage and type of cancer.

Traumatic and Vascular Causes

Physical trauma or abnormalities in blood vessels can also lead to distinct skin lesions.

Trauma and Injury: Acute injuries, such as cuts, scrapes (abrasions), and burns, are common causes of secondary lesions like erosions and ulcers. Chronic, repetitive trauma or pressure can lead to pressure ulcers (bedsores) in immobile patients.Healing involves wound care, preventing infection, and removing continuous pressure. The formation of a scar is the final result of the wound healing process involving the dermis.
Vascular Lesions: These are abnormalities of the blood vessels. Examples include Petechiae (small, non-blanching red/purple macules, <2 mm, indicating capillary bleeding) and Purpura (larger petechiae, >2 mm). These lesions do not turn white when pressed (non-blanching), indicating blood leakage outside the vessel wall.Non-blanching lesions suggest a potential problem with blood clotting, small vessel inflammation (vasculitis), or trauma. Further systemic workup is often required, particularly if the lesions are widespread.
Stasis Dermatitis: This is a condition affecting the lower legs due to chronic venous insufficiency, where blood pools in the veins. It presents as an erythematous, scaly, and often hyperpigmented patch or plaque, leading to edema and sometimes ulceration (venous stasis ulcers).Management focuses on reducing edema through compression stockings, elevation, and topical steroids to manage the associated inflammation and itching.

Diagnosis of Skin Lesions: A Step-by-Step Approach

The diagnosis of a skin lesion is a process that combines patient history, a detailed physical examination, and, when necessary, diagnostic procedures.

Step 1: History and Risk Assessment

The first step involves a comprehensive patient interview. Key questions address:

Onset and duration: When did the lesion first appear? Has it changed over time?
Symptoms: Is the lesion painful, itchy (pruritic), or burning?
Location: Where on the body did it start, and has it spread?
History: Has the patient traveled recently, been exposed to allergens, started new medications, or had contact with others with similar lesions?
Systemic symptoms: Does the patient have fever, joint pain, or other symptoms that might suggest a systemic disease?
Risk factors: History of excessive sun exposure, family history of skin cancer, or immunocompromised status.

This history helps narrow down the vast list of potential diagnoses. A lesion that has been present for years is less likely to be an acute infection but more likely to be a benign or slow-growing neoplasm.

Step 2: Physical Examination and Morphology Description

The physical examination is the core of dermatologic diagnosis. The practitioner examines the entire skin surface, not just the reported lesion, as some conditions are widespread. Crucially, the lesion is characterized using the precise terminology of primary and secondary lesions (macule, papule, plaque, etc.). The following characteristics are meticulously documented:

Color: The color can indicate etiology, such as black/brown (pigmented/melanocytic), blue/grey (deep pigmentation or drug reaction), red (erythematous/inflammatory or vascular), or yellow (fatty or lipid deposits).For instance, a “port-wine stain” is a vascular lesion with a distinctive reddish-purple color, while the “ash-leaf spot” of tuberous sclerosis is hypopigmented (lighter than the surrounding skin).
Shape and Arrangement: Lesions can be circular (annular, e.g., ringworm), linear (e.g., in a distribution of nerve dermatome, as in shingles), grouped (herpetiform, e.g., herpes simplex), or scattered (discrete).The pattern provides strong clues. For example, lesions following scratch marks (the Koebner phenomenon) are highly suggestive of psoriasis or lichen planus.
Texture: The texture is described as smooth, rough (verrucous, e.g., warts), pebbly, or indurated (hardened). The presence of scale, crust, or ulceration is also noted.Palpation is essential here; feeling a firm, subcutaneous nodule immediately rules out most primary epidermal lesions like macules or papules.
Distribution: The location on the body is highly significant. Psoriasis favors extensor surfaces (elbows, knees), while atopic dermatitis favors flexural surfaces (inner elbows, back of knees). Sun-exposed areas suggest photosensitivity or sun damage.Certain distributions are pathognomonic; for instance, the “Christmas tree” pattern of rash on the back is classic for Pityriasis Rosea.
Special Tests: Simple in-office tests like diascopy (pressing a glass slide on the lesion to see if it blanches) or a Wood’s light examination (ultraviolet light to reveal fluorescent organisms like fungi or bacteria) can be performed.A non-blanching lesion suggests extravasated blood (purpura), indicating a need for a deeper systemic workup.

Step 3: Diagnostic Procedures

When the diagnosis is unclear after history and physical examination, a procedure is often necessary to confirm the suspected condition.

Biopsy (Skin Biopsy): This is the definitive diagnostic tool for many lesions, especially those suspected to be malignant, infectious, or inflammatory. A small sample of tissue is removed and sent to a pathologist for microscopic examination. There are different types:A Shave Biopsy removes only the superficial skin layers (epidermis and superficial dermis) and is suitable for most non-melanoma skin cancers (BCC/SCC), seborrheic keratoses, and papillomatous lesions. A Punch Biopsy uses a circular instrument to take a deeper sample, including the epidermis, dermis, and sometimes subcutaneous fat, and is essential for diagnosing inflammatory conditions (vasculitis, autoimmune diseases) or deep nodules. An Excisional Biopsy removes the entire lesion and a margin of surrounding tissue and is the preferred method when melanoma is strongly suspected.
Dermoscopy: This is a non-invasive technique that uses a handheld magnifying device with a light source to examine skin lesions, particularly pigmented ones, at high magnification. It allows the practitioner to visualize subsurface structures and patterns invisible to the naked eye.Dermoscopy significantly improves the diagnostic accuracy for melanoma and other pigmented lesions, often preventing unnecessary biopsies of benign moles.
Culture and Sensitivity: If a bacterial or fungal infection is suspected, a swab or scrape from the lesion is sent to the lab to grow the organism (culture) and determine which medications will effectively kill it (sensitivity testing).This test is crucial for guiding antibiotic or antifungal treatment, especially in cases of recurrent or unresponsive infections, to prevent antibiotic resistance.
Tzanck Smear: A simple, rapid test where the base of a freshly opened blister or vesicle is scraped and the cells are examined under a microscope. The finding of multinucleated giant cells is highly suggestive of a herpes virus infection (herpes simplex or herpes zoster), although it does not differentiate between the two viruses.While less common now, this quick bedside test can provide immediate information, allowing for rapid initiation of antiviral therapy.

Treatment and Management of Skin Lesions

Treatment depends entirely on the definitive diagnosis and the severity of the lesion. It can range from simple observation and topical applications to systemic medications or surgical intervention.

Topical Treatments for Inflammatory Lesions

Topical Corticosteroids: These are the most common anti-inflammatory agents used to treat eczema, dermatitis, and localized psoriasis. They come in varying strengths (low to ultra-high potency) and vehicles (creams, ointments, lotions).
Topical Calcineurin Inhibitors (e.g., Tacrolimus, Pimecrolimus): Used for inflammation, particularly on sensitive areas (face, intertriginous areas) where prolonged corticosteroid use could cause skin thinning.
Topical Antifungals (e.g., Ketoconazole, Terbinafine): Used to treat localized fungal infections like ringworm and tinea versicolor.
Topical Antibiotics (e.g., Mupirocin): Used for localized bacterial infections like impetigo or for decolonization of Staphylococcus aureus in the nose.
Topical Retinoids (e.g., Tretinoin): Used to treat acne and sometimes for the prevention and treatment of actinic keratosis by promoting cell turnover.

Systemic Treatments for Widespread or Severe Lesions

When the lesions are widespread, fail to respond to topical therapy, or are a manifestation of a systemic disease, oral or injectable medications are necessary.

Oral Antibiotics and Antivirals: Oral antibiotics (e.g., Doxycycline, Cephalexin) are used for severe skin infections (cellulitis) or moderate-to-severe inflammatory acne. Oral antivirals (e.g., Acyclovir, Valacyclovir) are used to treat systemic viral infections like shingles or severe recurrent herpes simplex infections.The duration of therapy is critical to ensure complete eradication of the pathogen and prevent recurrence or development of resistance.
Oral Immunosuppressants and Biologics: For severe autoimmune and inflammatory conditions like widespread psoriasis or severe eczema, systemic immunosuppressants (ee.g., Methotrexate, Cyclosporine) or advanced biologic therapies (e.g., TNF-alpha inhibitors, IL-17/IL-23 inhibitors) are utilized.These treatments target specific components of the immune system that drive the inflammation, offering significant relief but requiring careful monitoring for side effects.
Oral Antihistamines: Used for symptomatic relief of pruritus (itching) associated with inflammatory lesions, such as urticaria, eczema, or insect bites. Non-sedating versions are preferred for daytime use, while sedating versions can aid sleep.Addressing the symptom of itching is critical because scratching leads to secondary lesions (excoriations and lichenification), perpetuating the itch-scratch cycle.

Surgical and Procedural Treatments

For neoplastic and certain benign lesions, physical removal or destruction of the abnormal tissue is often required.

Excision: Surgical removal (excision) is the standard treatment for malignant melanoma and most non-melanoma skin cancers (BCC and SCC). The lesion is cut out entirely, along with a specified margin of surrounding healthy tissue to ensure complete removal.The specimen is sent to a pathologist to confirm the diagnosis, check the depth of the cancer, and ensure the surgical margins are clear of tumor cells.
Cryotherapy: This involves using extreme cold, typically liquid nitrogen, to destroy abnormal tissue. It is a common and highly effective treatment for common warts, seborrheic keratoses, and actinic keratoses.The procedure is quick and done in the office, but it can cause temporary blistering and a change in skin pigmentation at the site of treatment.
Curettage and Electrodesiccation: A technique where the abnormal tissue is scraped off with a sharp, spoon-shaped instrument (curette), and the base is then burned with an electrical current (electrodesiccation) to stop bleeding and destroy any remaining tumor cells.This method is frequently used for superficial basal cell carcinomas and squamous cell carcinomas, as well as for removing certain benign lesions.
Laser Therapy and Photodynamic Therapy (PDT): Laser therapy uses focused light energy to treat various lesions, including vascular birthmarks (e.g., port-wine stains), prominent blood vessels, and some benign growths. PDT involves applying a topical photosensitizing agent to the lesion, which is then activated by a specific wavelength of light to selectively destroy the abnormal cells.PDT is a highly effective field treatment for actinic keratoses and is also used for some superficial skin cancers.

Pictures and Self-Examination: The ABCDEs of Melanoma Detection

While professional diagnosis is always required, routine skin self-examination is a powerful tool for early detection of potentially dangerous lesions, especially melanoma. The American Academy of Dermatology recommends using the ABCDE rule to look for changes in moles or the appearance of new, suspicious lesions.

A for Asymmetry: One half of the lesion does not match the other half.
B for Border: The borders are irregular, ragged, notched, or blurred. Benign moles usually have smooth, well-defined borders.
C for Color: The color is not uniform and may include shades of black, brown, tan, white, red, or blue.
D for Diameter: The diameter is typically larger than 6 millimeters (about the size of a pencil eraser), though melanomas can sometimes be smaller.
E for Evolving: The lesion is changing in size, shape, color, or elevation, or it starts to bleed, itch, or crust.

Conclusion

The vast array of skin lesions, from the common macule to the dangerous melanoma, underscores the complexity and importance of the skin as a diagnostic window to overall health. Accurate identification relies on meticulous history-taking and physical examination, utilizing the precise classification of primary and secondary morphology. While many lesions are benign and require minimal intervention, the potential for infectious, systemic, or malignant causes demands that any suspicious, changing, or persistent lesion be evaluated by a healthcare professional.

Treatment strategies are highly personalized, ranging from topical medications for inflammatory conditions to sophisticated surgical and photodynamic therapies for neoplastic lesions. Through continuous education on lesion types, diligent self-examination using the ABCDE rule, and prompt consultation for any abnormality, individuals can ensure early diagnosis and the best possible health outcomes. Understanding the types, causes, diagnosis, and treatment of skin lesions is an essential step in maintaining lifelong skin and general health.