Dermatology Guide: Skin Assessment, Psoriasis Scoring, Burn Evaluation, and Melanoma Detection

What Is Dermatology?

Dermatology is the branch of medicine concerned with the diagnosis and treatment of skin, hair, nail, and mucous membrane disorders. The skin is the body's largest organ, covering approximately 1.7 square meters in adults. Dermatologists manage more than 3,000 distinct skin conditions—from inflammatory disorders like psoriasis and eczema to skin cancers, including melanoma, which accounts for the majority of skin cancer deaths despite representing only 1% of cases.

How Is Skin Health Maintained?

The skin is the body's largest organ, accounting for approximately 15 percent of total body weight and covering an average surface area of about 1.7 square meters in adults. Far from being a passive wrapper, the skin is a dynamic, metabolically active organ that serves as the primary barrier against infection, ultraviolet radiation, chemical exposure, and physical injury. It regulates body temperature through sweating and blood vessel dilation, synthesizes vitamin D in response to sunlight, and contains an extensive network of sensory nerve endings that detect touch, pain, temperature, and pressure.

The skin consists of three principal layers. The epidermis is the outermost layer, composed primarily of keratinocytes that continuously divide, migrate upward, and eventually shed. The epidermis also contains melanocytes (which produce the pigment melanin), Langerhans cells (immune sentinels), and Merkel cells (involved in touch sensation). The dermis lies beneath and provides structural support through collagen and elastin fibers, houses blood vessels, nerves, hair follicles, and sweat glands. The hypodermis (subcutaneous layer) consists mainly of fat tissue that provides insulation, cushioning, and energy storage.

Skin diseases are among the most common reasons people seek medical care. They range from minor nuisances like dry skin and mild acne to serious, life-altering conditions such as psoriasis, severe burns, and skin cancer. This guide covers the major dermatological assessment tools used in clinical practice and provides context for understanding common skin conditions.

What Is Psoriasis and How Is It Scored?

Psoriasis is a chronic, immune-mediated inflammatory disease that affects approximately 2 to 3 percent of the global population. It is characterized by well-demarcated, raised, red plaques covered with silvery-white scales, most commonly found on the elbows, knees, scalp, and lower back. However, psoriasis can affect any area of the skin, including the nails, palms, soles, and genital region.

The underlying pathology involves an overactive immune response in which T cells and other immune cells trigger excessive proliferation of keratinocytes. Normal skin cells take about a month to mature and shed; in psoriatic skin, this process is compressed to just three to four days, resulting in a buildup of cells on the surface that forms the characteristic plaques. Psoriasis is not contagious. It has a strong genetic component, with multiple susceptibility genes identified, and is influenced by environmental triggers including stress, infections (particularly streptococcal throat infections), certain medications, and smoking.

The Psoriasis Area and Severity Index (PASI) is the most widely used tool for measuring psoriasis severity in clinical trials and increasingly in routine clinical practice. It evaluates four body regions -- head and neck, upper extremities, trunk, and lower extremities -- accounting for the percentage of each region affected and the severity of three plaque characteristics: erythema (redness), induration (thickness), and desquamation (scaling). Each characteristic is graded from 0 (none) to 4 (very severe).

The area of involvement in each body region is scored from 0 (no involvement) to 6 (90 to 100 percent involvement). These scores are combined using a weighted formula that accounts for the relative surface area of each body region (the lower extremities represent a larger proportion of body surface area than the head, for example). The total PASI score ranges from 0 to 72, though scores above 40 are rare.

In clinical practice, PASI scores are categorized as mild (below 7), moderate (7 to 12), and severe (above 12). Treatment goals typically aim for a PASI 75 response (75 percent reduction from baseline) or increasingly a PASI 90 or PASI 100 response, particularly with newer biologic therapies. A PASI score below 3 is often considered "clear" or "almost clear" skin.

Psoriasis is more than a skin disease. It is associated with psoriatic arthritis (affecting up to 30 percent of psoriasis patients), cardiovascular disease, metabolic syndrome, depression, and reduced quality of life. Comprehensive management addresses not only the skin but also these systemic comorbidities.

How Is Burn Extent Assessed?

Approximately 11 million burn injuries annually require medical attention worldwide, with 300,000 deaths per year; 90% of severe burn deaths occur in low- and middle-income countries where access to specialized burn centers is limited (WHO 2022). Burns are among the most physically and psychologically traumatic injuries a person can sustain. Accurate assessment of burn severity is critical for determining the appropriate level of care, calculating fluid resuscitation requirements, and predicting outcomes. The two most important parameters in burn assessment are the total body surface area (TBSA) affected and the depth of the burn.

Burn depth is classified into three categories. Superficial (first-degree) burns affect only the epidermis, causing redness and pain but no blistering (a typical sunburn). Partial-thickness (second-degree) burns extend into the dermis and are further divided into superficial partial-thickness (blistering, moist, painful) and deep partial-thickness (drier, less painful due to nerve damage, may require skin grafting). Full-thickness (third-degree) burns destroy the entire epidermis and dermis, appearing white, waxy, or charred, and are characteristically painless because sensory nerve endings have been destroyed.

The Wallace Rule of Nines is the most widely taught method for rapidly estimating burn TBSA in adults. It divides the body into regions that each represent approximately 9 percent (or multiples of 9) of the total body surface. The head and neck represent 9 percent, each upper extremity 9 percent, each lower extremity 18 percent (9 percent for the anterior surface, 9 percent for the posterior), the anterior trunk 18 percent, the posterior trunk 18 percent, and the perineum 1 percent. The patient's palm (including the fingers) represents approximately 1 percent of their TBSA and can be used to estimate smaller or irregularly shaped burns.

The Rule of Nines is quick and practical for initial field or emergency department assessment, but it has important limitations. It is less accurate for children, whose body proportions differ significantly from adults. An infant's head, for example, represents approximately 18 percent of TBSA (twice the adult proportion), while the lower extremities represent a smaller proportion. For this reason, the Lund-Browder chart was developed. It provides age-adjusted percentages for each body region and is considered the most accurate method for estimating burn TBSA across all age groups. It is the standard of care for formal burn assessment in burn centers.

Burns covering more than 10 percent TBSA in children or 15 to 20 percent TBSA in adults generally require intravenous fluid resuscitation, typically guided by the Parkland formula (4 mL of lactated Ringer's solution per kilogram of body weight per percent TBSA burned, administered over 24 hours). Burns involving the face, hands, feet, genitalia, major joints, or circumferential burns of the extremities are considered critical regardless of size and should be managed at a specialized burn center.

How Does Skin Disease Affect Quality of Life?

Skin conditions affect approximately 1.9 billion people worldwide at any given time; dermatological diseases represent the fourth leading cause of non-fatal disease burden globally (WHO GBD study). Skin diseases, even when not medically dangerous, can profoundly affect a person's quality of life. Visible skin conditions may cause embarrassment, social withdrawal, workplace discrimination, relationship difficulties, and psychological distress. Recognizing and measuring this impact is essential for providing truly patient-centered care.

The Dermatology Life Quality Index (DLQI) is the most widely used dermatology-specific quality of life instrument. Developed in 1994, it consists of 10 questions covering six domains: symptoms and feelings, daily activities, leisure, work and school, personal relationships, and treatment. Each question is scored from 0 (not at all affected) to 3 (very much affected), yielding a total of 0 to 30.

DLQI scores are interpreted as follows: 0 to 1 indicates no effect on quality of life, 2 to 5 a small effect, 6 to 10 a moderate effect, 11 to 20 a very large effect, and 21 to 30 an extremely large effect. A change of 4 or more points is considered clinically meaningful.

The DLQI has been incorporated into treatment guidelines for conditions like psoriasis, where it helps determine eligibility for biologic therapies. In many healthcare systems, patients must demonstrate a DLQI above a certain threshold (often 10) in addition to clinical severity measures to qualify for advanced treatments. This integration ensures that the patient's lived experience is valued alongside objective clinical measures.

It is worth noting that the DLQI has limitations. It may not fully capture the psychological burden of conditions like vitiligo or alopecia, where the physical symptoms are minimal but the cosmetic and psychosocial impact can be devastating. Complementary instruments, including the Skindex and disease-specific measures, may provide additional insight in such cases.

How Is Melanoma Detected?

Melanoma is the most dangerous form of skin cancer. While it accounts for only about 1 percent of skin cancers, it is responsible for the vast majority of skin cancer deaths. However, when detected early -- before it has penetrated deeply into the skin -- melanoma is highly curable, with five-year survival rates exceeding 99 percent for localized disease. Late-stage melanoma, by contrast, has a far grimmer prognosis, making early detection a matter of life and death.

The ABCDE criteria provide a systematic framework for evaluating pigmented skin lesions (moles and spots) for features that may suggest melanoma:

Asymmetry: If you draw an imaginary line through the middle of the lesion, the two halves should roughly mirror each other in a benign mole. Melanomas are often asymmetric, with one half looking different from the other in shape, color, or texture.

Border: Benign moles typically have smooth, well-defined borders. Melanomas often have irregular, ragged, notched, or blurred edges. The pigment may appear to fade into the surrounding skin without a clear boundary.

Color: A uniform color (usually a single shade of brown) is reassuring. Multiple colors within a single lesion -- especially combinations of brown, black, red, white, or blue -- raise concern for melanoma. Any area of very dark or black pigmentation warrants attention.

Diameter: Melanomas are typically larger than 6 millimeters (approximately the diameter of a pencil eraser) when diagnosed, though they can be smaller. Any growing lesion deserves evaluation regardless of its current size.

Evolution: This is perhaps the most important criterion. Any mole that is changing -- in size, shape, color, elevation, or any other characteristic -- or that develops new symptoms such as bleeding, itching, or crusting should be evaluated promptly. The "ugly duckling" sign is a related concept: a mole that looks different from all other moles on the same person deserves closer scrutiny, even if it does not meet other ABCDE criteria.

Not all melanomas follow the ABCDE pattern. Amelanotic (non-pigmented) melanomas, nodular melanomas, and subungual (under the nail) melanomas may present atypically. This is why regular skin examinations by a dermatologist are recommended for individuals at higher risk, including those with a history of sunburns, many moles, fair skin, a family history of melanoma, or prior skin cancer.

What Are the Most Common Skin Conditions?

Atopic dermatitis (eczema) affects approximately 15–20% of children and 1–3% of adults worldwide; contact dermatitis accounts for up to 90% of occupational skin disease, costing an estimated $1 billion annually in the United States alone. Beyond the conditions assessed by formal scoring tools, several common skin conditions are worth understanding.

Acne vulgaris is the most common skin condition, affecting up to 85 percent of adolescents and many adults. It results from clogged hair follicles due to excess sebum production, abnormal keratinization, bacterial colonization (particularly Cutibacterium acnes), and inflammation. Treatments range from topical retinoids and benzoyl peroxide for mild cases to oral antibiotics, hormonal therapies, and isotretinoin for severe disease.

Eczema (atopic dermatitis) is a chronic inflammatory condition characterized by itchy, red, dry skin. It often begins in childhood and is associated with a family history of atopy (eczema, asthma, or allergic rhinitis). Management centers on skin barrier restoration with moisturizers, topical anti-inflammatory agents (corticosteroids and calcineurin inhibitors), trigger avoidance, and newer biologic therapies for severe cases.

Skin infections, including bacterial (cellulitis, impetigo), fungal (athlete's foot, ringworm), and viral (warts, herpes simplex) infections, are exceedingly common and usually treatable with appropriate antimicrobial therapy.

How Does Sun Protection Prevent Skin Damage?

UV radiation exposure causes approximately 90% of non-melanoma skin cancers and 65–85% of melanomas; broad-spectrum SPF 30 sunscreen reduces squamous cell carcinoma risk by approximately 40% and melanoma risk by approximately 50% with regular use. Ultraviolet (UV) radiation from sunlight is the single most preventable risk factor for skin cancer and premature skin aging. UV radiation is classified into UVA (which penetrates deeply and contributes to aging and cancer) and UVB (which primarily causes sunburn and is a major contributor to skin cancer).

Evidence-based sun protection strategies include applying broad-spectrum sunscreen with an SPF of 30 or higher to exposed skin, reapplying every two hours and after swimming or sweating, seeking shade during peak UV hours (typically 10 a.m. to 4 p.m.), wearing protective clothing including wide-brimmed hats and UV-blocking sunglasses, and avoiding indoor tanning beds, which are classified as Group 1 carcinogens by the International Agency for Research on Cancer.

When to See a Dermatologist

While many skin concerns can be managed by primary care providers, certain situations warrant referral to a dermatologist: any new or changing mole (especially one meeting ABCDE criteria), a skin lesion that bleeds, does not heal, or grows rapidly, widespread or severe rashes not responding to initial treatment, suspected psoriasis or other chronic inflammatory skin conditions, severe acne (especially if scarring is developing), hair loss with an unclear cause, and any skin condition significantly affecting quality of life.

The assessment tools described in this guide are used by dermatologists and other clinicians to standardize evaluation, track disease progression, and guide treatment decisions. They serve as useful educational references for patients seeking to understand their condition better, but they are not substitutes for professional clinical evaluation.