Dermatologic disorders affect the skin, hair, nails, and mucous membranes. The skin is the largest organ, serving as a barrier against pathogens, ultraviolet radiation, and water loss. Dermatologic disease accounts for substantial morbidity and healthcare utilization, and can be a window to systemic disease.
Acne Vulgaris
Acne is the most common skin condition, affecting nearly all adolescents and persisting into adulthood in many. Four pathogenic factors: increased sebum production (androgen-driven), follicular hyperkeratinization, Cutibacterium acnes colonization, and inflammation.
Clinical features. Non-inflammatory: open comedones (blackheads) and closed comedones (whiteheads). Inflammatory: papules, pustules, nodules, and cysts. Distribution: face, chest, and back. Post-inflammatory hyperpigmentation and scarring are important sequelae.
Treatment. Mild: topical retinoids (adapalene, tretinoin), benzoyl peroxide, and topical antibiotics (clindamycin). Moderate: combination topical therapy plus oral antibiotics (doxycycline, minocycline) or hormonal therapy (combined oral contraceptive, spironolactone). Severe: isotretinoin, a retinoid that targets all four pathogenic factors. Isotretinoin requires monitoring for teratogenicity, mood changes, and laboratory abnormalities.
Atopic Dermatitis (Eczema)
A chronic, pruritic, inflammatory skin disease driven by epidermal barrier dysfunction (filaggrin mutations) and type 2 immune dysregulation (IL-4, IL-13). Affects 15–20% of children and 7–10% of adults.
Clinical features. Intense pruritus, erythematous papules, xerosis (dry skin), lichenification (thickened skin from chronic scratching). Distribution: flexural (antecubital and popliteal fossae) in children and adults; face and extensor surfaces in infants. Often associated with asthma, allergic rhinitis, and food allergy (atopic march).
Treatment. Emollients (moisturizers) are foundational. Topical corticosteroids (stepwise potency) are first-line anti-inflammatory therapy. Topical calcineurin inhibitors (tacrolimus, pimecrolimus) are steroid-sparing alternatives. For moderate to severe disease: phototherapy (narrowband UVB), systemic immunosuppressants (cyclosporine, methotrexate, mycophenolate), and biologics (dupilumab — anti-IL-4Rα, tralokinumab — anti-IL-13). Crisaborole (PDE4 inhibitor) and ruxolitinib (JAK inhibitor) are topical options.
Psoriasis
A chronic immune-mediated inflammatory skin disease affecting 2–3% of the global population. The IL-23/Th17 axis drives keratinocyte hyperproliferation and inflammation.
Clinical features. Well-demarcated, erythematous plaques with silvery scale on the scalp, elbows, knees, and sacrum. Nail changes: pitting, onycholysis, oil spots. Inverse psoriasis: intertriginous involvement. Guttate psoriasis: acute eruption of small plaques triggered by streptococcal infection. Pustular and erythrodermic psoriasis are severe variants.
Psoriatic arthritis. An inflammatory arthritis associated with psoriasis, affecting 20–30% of patients. Five patterns: oligoarticular, polyarticular, distal interphalangeal, spondylitis, and arthritis mutilans. Treatment (see below) addresses both skin and joints.
Treatment. Mild: topical corticosteroids, vitamin D analogs (calcipotriene), and tazarotene. Moderate to severe: phototherapy (NB-UVB, PUVA), methotrexate, cyclosporine, and acitretin. Biologics targeting TNF (adalimumab, infliximab), IL-17 (secukinumab, ixekizumab, brodalumab), IL-23 (guselkumab, risankizumab, tildrakizumab), and IL-12/23 (ustekinumab). Oral small molecules: apremilast (PDE4 inhibitor), deucravacitinib (TYK2 inhibitor).
Skin Infections
Bacterial. Impetigo (superficial, honey-colored crusts, caused by Staph aureus or Strep pyogenes) — topical mupirocin. Cellulitis (deep dermal/subcutaneous infection with erythema, warmth, swelling, tenderness) — oral or IV antibiotics targeting Strep and Staph. MRSA requires appropriate coverage.
Viral. Herpes simplex (oral, genital, herpetic whitlow) — antiviral therapy (acyclovir, valacyclovir). Varicella zoster (chickenpox, shingles) — vaccination is highly effective; antivirals within 72 hours reduce acute pain and postherpetic neuralgia. Molluscum contagiosum — self-limited, cryotherapy or curettage if needed. Human papillomavirus (common warts, genital warts) — cryotherapy, salicylic acid, imiquimod.
Fungal. Dermatophytosis (tinea corporis, tinea cruris, tinea pedis, tinea capitis) — topical or systemic antifungals (terbinafine, azoles). Candidiasis (intertriginous, oral thrush, vulvovaginal) — azoles.
Blistering Disorders
Pemphigus vulgaris. Autoantibodies against desmoglein 3 (and 1) cause intraepidermal acantholysis and fragile blisters. Mucous membrane involvement is common and severe. Treatment: high-dose corticosteroids, rituximab, and immunosuppressants.
Bullous pemphigoid. Autoantibodies against BP180 and BP230 cause subepidermal blisters. Tense blisters on flexural skin; mucosal involvement is mild. Less aggressive than pemphigus. Treatment: potent topical or systemic corticosteroids, doxycycline, and immunosuppressants.
Pigmentary Disorders
Vitiligo. Autoimmune destruction of melanocytes causes depigmented patches. Treatment: topical corticosteroids, topical calcineurin inhibitors, narrowband UVB phototherapy, and JAK inhibitors (ruxolitinib cream). Surgical grafting for stable disease.
Melasma. Hyperpigmentation on the face, triggered by UV exposure, pregnancy, and hormonal contraceptives. Treatment: sun protection (foundational), topical hydroquinone, tretinoin, azelaic acid, and tranexamic acid.
Hair and Nail Disorders
Alopecia areata. Autoimmune, non-scarring hair loss in patches. May progress to total loss of scalp hair (alopecia totalis) or body hair (alopecia universalis). Treatment: intralesional corticosteroids, topical sensitizers (DPCP), and JAK inhibitors (baricitinib, ritlecitinib).
Androgenetic alopecia. Pattern hair loss in men (vertex and bitemporal) and women (crown thinning). Driven by dihydrotestosterone. Treatment: topical minoxidil, oral finasteride, low-level laser therapy, and hair transplantation.
Nail disorders. Onychomycosis (fungal nail infection) — oral terbinafine. Ingrown toenails — conservative care or partial nail avulsion. Nail changes in psoriasis and lichen planus are diagnostic clues.
Summary
Dermatologic disorders encompass the full spectrum from common conditions (acne, eczema, psoriasis) to life-threatening malignancies (melanoma) and rare autoimmune blistering diseases. Acne and eczema are driven by distinct mechanisms — follicular hyperkeratinization versus barrier dysfunction — but both respond to topical therapies. Psoriasis is a systemic inflammatory disease with joint involvement. Skin cancer is largely preventable through sun protection. Autoimmune blistering diseases require aggressive immunosuppression. Across all dermatologic conditions, the physical examination — aided by dermoscopy and biopsy — remains the cornerstone of diagnosis.