Dermatologic conditions encompass a wide range of disorders affecting the skin, hair, nails, and mucous membranes. They are among the most common medical conditions, affecting virtually everyone at some point in life. This article provides comprehensive coverage of major dermatologic conditions.
Acne Vulgaris
| Parameter | Detail |
|---|---|
| Definition | Chronic inflammatory disease of pilosebaceous units characterized by comedones, papules, pustules, nodules, and potentially scarring |
| Prevalence | 85% of adolescents (ages 12-24); can persist into adulthood |
| Pathophysiology | Four factors: increased sebum production (androgen-driven), hyperkeratinization of follicular epithelium (retention hyperkeratosis), Cutibacterium acnes colonization, inflammation |
Acne Severity Classification
| Severity | Lesion Type | Distribution | Scarring |
|---|---|---|---|
| Mild | Comedones (open/closed), few papules/pustules | Localized | None or minimal |
| Moderate | Multiple papules/pustules, few nodules | Facial, back, chest | Possible |
| Severe | Nodules, cysts, extensive papules/pustules | Widespread | Common |
| Very severe | Nodulocystic conglobata, sinus tracts | Extensive | Severe scarring |
Acne Treatment
| Type | Mild | Moderate | Severe |
|---|---|---|---|
| Comedonal | Topical retinoid (tretinoin, adapalene, tazarotene) | Topical retinoid + benzoyl peroxide | Oral antibiotic + topical retinoid + benzoyl peroxide |
| Inflammatory | Topical retinoid + benzoyl peroxide OR topical antibiotic (clindamycin, erythromycin) | Topical retinoid + benzoyl peroxide + topical antibiotic + oral antibiotic (doxycycline, minocycline, sarecycline) | Oral antibiotic + topical retinoid + benzoyl peroxide; consider isotretinoin |
| Hormonal (women) | OCP (drospirenone/ethinyl estradiol, norgestimate), spironolactone | Same | Same + others |
| Refractory | – | – | Isotretinoin (13-cis-retinoic acid) - most effective, requires monitoring (pregnancy, lipids, LFTs) |
| Physical | Comedone extraction | Chemical peels, light/laser therapy | Drainage of cysts, intralesional triamcinolone |
Atopic Dermatitis (Eczema)
| Parameter | Detail |
|---|---|
| Definition | Chronic, relapsing inflammatory skin disease characterized by intense pruritus and eczematous lesions |
| Prevalence | 15-20% of children, 3-5% of adults |
| Pathophysiology | Skin barrier dysfunction (filaggrin mutation in 30%), Th2-dominated inflammation (IL-4, IL-13, IL-31), altered skin microbiome (S. aureus colonization), immune dysregulation |
Atopic Dermatitis Stages and Distribution
| Stage | Age | Distribution | Lesion Morphology |
|---|---|---|---|
| Infantile | 2 months - 2 years | Face (cheeks, forehead), scalp, extensor extremities | Erythema, vesicles, weeping, crusting |
| Childhood | 2-12 years | Flexural (antecubital, popliteal), neck, wrists, ankles | Lichenification, papules, dry skin |
| Adult | >12 years | Flexural, hands, face, neck, upper body | Lichenification, prurigo nodules, xerosis |
Atopic Dermatitis Severity
| Parameter | Mild | Moderate | Severe |
|---|---|---|---|
| Body surface area | <5% | 5-20% | >20% |
| Pruritus | Mild, intermittent | Moderate, frequent | Severe, constant, sleep disturbance |
| Eczema Area and Severity Index (EASI) | <7 | 7-21 | >21 |
| Impact on quality of life | Minimal | Moderate | Severe |
Atopic Dermatitis Treatment
| Step | Intervention | Notes |
|---|---|---|
| 1 | Emollients/moisturizers (fragrance-free, thick creams/ointments), gentle skin care, avoid triggers | Apply within 3 minutes of bathing; use at least 2x/day |
| 2 | Topical corticosteroids (TCS) - mild (class 6-7) for face/flexures, moderate-strong (class 2-4) for trunk/extremities | Use BID for flares, then taper; avoid prolonged high-potency on face, groin, axillae |
| 3 | Topical calcineurin inhibitors (TCI): tacrolimus, pimecrolimus | Second-line for sensitive areas (face, neck, flexures); no atrophy; black box warning (rare lymphoma) |
| 4 | Phototherapy (NB-UVB, UVA1) | For moderate-severe, steroid-sparing; requires dedicated visits |
| 5 | Systemic immunosuppression: cyclosporine (first-line, rapid onset), methotrexate, azathioprine, mycophenolate mofetil | For severe refractory; monitor side effects |
| 6 | Biologics: dupilumab (IL-4R alpha), tralokinumab (IL-13), lebrikizumab (IL-13) | Approved for moderate-severe; highly effective, well-tolerated |
| 7 | JAK inhibitors: upadacitinib, abrocitinib | Oral for moderate-severe; rapid onset; VZV, thrombosis, LFT monitoring |
| Infection | Antiseptics (dilute bleach baths), topical antibiotics (mupirocin for S. aureus), systemic antibiotics if widespread | Bleach baths 2-3x/week can reduce S. aureus colonization |
Psoriasis
| Parameter | Detail |
|---|---|
| Definition | Chronic immune-mediated inflammatory disease primarily affecting skin and joints with characteristic well-demarcated, erythematous, scaly plaques |
| Prevalence | 2-3% of population; equal sex distribution; bimodal age of onset (16-22, 57-60) |
| Pathophysiology | Th1/Th17-mediated inflammation (IL-23, IL-17, TNF-alpha), hyperproliferation of keratinocytes (epidermal turnover from 28 days to 3-5 days), genetic predisposition (PSORS loci, HLA-Cw6) |
Psoriasis Types
| Type | Frequency | Distribution | Features |
|---|---|---|---|
| Plaque psoriasis (psoriasis vulgaris) | 80-90% | Scalp, elbows, knees, lumbosacral, extensor extremities | Well-demarcated erythematous plaques with silvery scale; Koebner phenomenon (lesions at trauma sites) |
| Guttate psoriasis | 10% | Trunk, proximal extremities (diffuse, drop-like) | Sudden onset after streptococcal pharyngitis in children/young adults; often remits |
| Inverse (flexural) psoriasis | 5-10% | Intertriginous areas (axillae, groin, inframammary, gluteal cleft) | Erythematous, smooth, shiny plaques (no scale due to moisture) |
| Pustular psoriasis | Rare | Generalized (von Zumbusch) or localized (palms/soles) | Sterile pustules on erythematous base; can be life-threatening (generalized) |
| Erythrodermic psoriasis | Rare | >90% body surface area | Generalized erythema, scaling, pruritus, fever, hypothermia, dehydration; medical emergency |
| Nail psoriasis | 50% of psoriasis patients | Fingernails/toenails | Pitting, onycholysis, subungual hyperkeratosis, oil drop sign (salmon patch) |
Psoriasis Severity
| Severity | BSA | PASI | DLQI | Treatment |
|---|---|---|---|---|
| Mild | <5% | <10 | <10 | Topical therapy |
| Moderate | 5-20% | 10-20 | 10-18 | Phototherapy, systemic therapy |
| Severe | >20% | >20 | >18 | Systemic therapy, biologics |
Psoriasis Treatment
| Modality | Examples | Notes |
|---|---|---|
| Topical corticosteroids | Betamethasone, clobetasol, triamcinolone, hydrocortisone | First-line for mild-moderate; use potent for trunk/extremities, mild for face/flexures |
| Topical vitamin D analogs | Calcipotriene, calcitriol | First-line for mild-moderate; can combine with topical steroids |
| Topical calcineurin inhibitors | Tacrolimus, pimecrolimus | For face, intertriginous areas, perineum |
| Topical retinoid | Tazarotene | For stable plaque psoriasis |
| Coal tar | Various preparations | Less common now |
| Anthralin | – | Less common now |
| Phototherapy | NB-UVB, PUVA (psoralen + UVA), excimer laser | For moderate-severe; PUVA has increased skin cancer risk |
| Oral systemic | Methotrexate, cyclosporine, acitretin, apremilast (PDE4 inhibitor) | For moderate-severe; apremilast is well-tolerated but less effective |
| TNF inhibitors | Adalimumab, etanercept, infliximab | First-line biologics for moderate-severe |
| IL-17 inhibitors | Secukinumab, ixekizumab, brodalumab | Highly effective, rapid onset; caution in IBD (may worsen) |
| IL-23 inhibitors | Ustekinumab (p40), guselkumab, risankizumab, tildrakizumab | Highly effective, durable response, good safety profile |
| IL-12/23 inhibitor | Ustekinumab | First/second-line biologic |
Rosacea
| Parameter | Detail |
|---|---|
| Definition | Chronic inflammatory skin condition affecting the central face (cheeks, nose, chin, forehead) characterized by flushing, erythema, telangiectasias, papules, pustules, and sometimes ocular involvement |
| Prevalence | 5-10% of population; more common in fair-skinned individuals (Fitzpatrick I-II), peak age 30-50 |
| Pathophysiology | Dysregulation of innate immune system (TLR2, LL-37/cathelicidin), neurovascular dysregulation (flushing), Demodex mites, UV damage, H. pylori association |
Rosacea Subtypes
| Subtype | Features | Treatment |
|---|---|---|
| Erythematotelangiectatic (ETR) | Flushing, persistent central facial erythema, telangiectasias | Avoid triggers (sun, heat, spicy foods, alcohol); topical brimonidine/oxymetazoline (vasoconstrictor), IPL/laser for telangiectasias |
| Papulopustular | Persistent erythema + papules and pustules (no comedones) | Topical: metronidazole, ivermectin, azelaic acid; Oral: doxycycline (sub-antimicrobial dose 40 mg/day), minocycline |
| Phymatous | Thickened skin, irregular contours (rhinophyma - most common) | Laser therapy, dermabrasion, electrosurgery, surgical shave excision |
| Ocular | Dry eyes, blepharitis, conjunctivitis, keratitis, styes | Warm compresses, lid hygiene, artificial tears, topical cyclosporine, oral doxycycline |
Urticaria (Hives)
| Parameter | Detail |
|---|---|
| Definition | Pruritic, erythematous, edematous wheals (raised lesions) that are transient (<24 hours per lesion) due to mast cell degranulation |
| Classification | Acute (<6 weeks, often allergic) vs Chronic (>6 weeks, often idiopathic) |
| Pathophysiology | Mast cell activation -> histamine, leukotrienes, prostaglandins -> vasodilation, increased vascular permeability -> wheal and flare |
| Common triggers (acute) | Foods (nuts, shellfish, eggs, milk, soy, wheat), drugs (NSAIDs, antibiotics, ACEi), infections, insect stings, physical (cold, heat, pressure, exercise, vibration, cholinergic, aquagenic, solar, dermatographism) |
| Chronic urticaria | Often idiopathic (90%); autoimmune (30-50%: anti-Fc-epsilon-RI or anti-IgE autoantibodies), physical, or associated with thyroid disease, infections, malignancy (rare) |
Urticaria Treatment
| Step | Drug | Dose | Notes |
|---|---|---|---|
| 1 | Second-generation H1 antihistamines | Cetirizine 10-20 mg, levocetirizine 5 mg, loratadine 10 mg, fexofenadine 180 mg, bilastine 20 mg | First-line; daily rather than PRN; up to 4x standard dose recommended (EAACI/GA2LEN guidelines) |
| 2 | Add H2 antihistamine | Famotidine 20-40 mg BID | Modest additional benefit |
| 3 | Add leukotriene receptor antagonist | Montelukast 10 mg daily | More effective for NSAID-induced and autoimmune urticaria |
| 4 | Add first-generation H1 antihistamine at bedtime | Hydroxyzine, doxepin | For severe, persistent symptoms; sedation may be useful |
| 5 | Omalizumab (anti-IgE) | 150-300 mg SC q4 weeks | Highly effective for chronic spontaneous urticaria (CSU) |
| 6 | Cyclosporine | 3-5 mg/kg/day | For severe, refractory CSU; requires monitoring (BP, renal) |
| Acute severe urticaria/angioedema | Epinephrine IM (0.3 mg auto-injector) + prednisone 40-60 mg x3-5 days + H1 antihistamine | For anaphylaxis/laryngeal edema |
Skin Infections
Bacterial Infections
| Infection | Pathogen | Presentation | Treatment |
|---|---|---|---|
| Impetigo | S. pyogenes, S. aureus | Honey-colored crusted lesions (non-bullous) or thin-roofed bullae (bullous), perioral/nasal | Topical mupirocin or retapamulin (mild); cephalexin, clindamycin (extensive) |
| Cellulitis | S. pyogenes, S. aureus | Spreading erythema, warmth, edema, tenderness; lower leg most common | Cephalexin (mild), cefazolin/ceftriaxone (moderate), vancomycin if MRSA risk |
| Erysipelas | S. pyogenes (Group A Strep) | Well-demarcated, raised, bright red, painful plaque with fever; face or lower leg | Penicillin or amoxicillin |
| Folliculitis | S. aureus (most common), Pseudomonas (hot tub) | Pustules at hair follicles | Topical clindamycin or mupirocin; cephalexin if extensive |
| Furuncle (boil) | S. aureus | Deep folliculitis -> abscess | Warm compresses, I&D; antibiotics if surrounding cellulitis or immunocompromised |
| Carbuncle | S. aureus | Aggregation of furuncles, deeper, systemic symptoms | I&D + antibiotics (TMP-SMX, doxycycline, clindamycin) |
Fungal Infections
| Infection | Pathogen | Clinical Features | Diagnosis | Treatment |
|---|---|---|---|---|
| Tinea pedis (athlete’s foot) | T. rubrum, T. mentagrophytes, E. floccosum | Interdigital maceration/scale, moccasin distribution (hyperkeratosis), vesiculobullous | KOH prep: hyphae | Topical terbinafine, clotrimazole; oral terbinafine or itraconazole (if refractory/extensive) |
| Tinea corporis (ringworm) | T. rubrum, M. canis | Annular plaque with raised, scaling border, central clearing; pruritic | KOH prep | Topical terbinafine, clotrimazole; oral if widespread |
| Tinea cruris (jock itch) | T. rubrum, E. floccosum | Groin, inner thighs (spares scrotum), well-demarcated, scaling, pruritic | KOH prep | Topical terbinafine, clotrimazole (avoid potent steroids - can worsen) |
| Tinea capitis (scalp ringworm) | T. tonsurans (US), M. canis | Patches of alopecia with broken hairs (black dot), scaling, inflammation (kerion) | KOH prep, fungal culture, Wood lamp (ectothrix fluoresces) | Oral griseofulvin or terbinafine (topicals ineffective for hair shaft); selenium sulfide shampoo to reduce shedding |
| Tinea versicolor (pityriasis versicolor) | Malassezia globosa, M. furfur | Hypopigmented or hyperpigmented macules on trunk, fine scale (positive when scraped) | KOH prep: spaghetti and meatballs (yeast + short hyphae) | Topical ketoconazole, selenium sulfide, terbinafine; oral fluconazole or itraconazole (if extensive) |
| Onychomycosis (nail fungus) | T. rubrum (most common), T. mentagrophytes, Candida | Distal lateral subungual, superficial white, proximal subungual, total dystrophic | KOH + culture or PAS (most sensitive) | Oral terbinafine (first-line, 12 weeks for toenails, 6 weeks for fingernails); topical efinaconazole, tavaborole (mild-moderate); laser (limited evidence) |
| Candidal intertrigo | Candida albicans | Moist, erythematous, satellite papules/pustules in intertriginous areas | KOH prep: pseudohyphae + budding yeast | Topical clotrimazole, miconazole, nystatin; drying powder; oral fluconazole if severe |
Viral Infections
| Infection | Pathogen | Clinical Features | Treatment |
|---|---|---|---|
| Herpes simplex (HSV-1, HSV-2) | HSV-1 (orolabial), HSV-2 (genital) | Grouped vesicles on erythematous base, prodrome (tingling, burning), recurrent | Acyclovir, valacyclovir, famciclovir (oral/topical/IV); suppressive therapy for frequent recurrences |
| Herpes zoster (shingles) | VZV (reactivation) | Unilateral vesicular eruption in dermatomal distribution, severe pain (precedes rash), post-herpetic neuralgia | Acyclovir, valacyclovir, famciclovir (within 72 hours of rash); analgesics; RZV vaccine for prevention |
| Varicella (chickenpox) | VZV (primary) | Pruritic vesicular eruption (dew drops on rose petals), fever, malaise; generalized | Supportive (calamine, antihistamines); acyclovir if severe/adult/immunocompromised |
| Warts (verruca) | HPV (multiple types) | Hyperkeratotic papules: common (hands), plantar (feet - deep, painful), flat (face), genital (condyloma acuminata) | Salicylic acid, cryotherapy, cantharidin, laser, topical imiquimod (genital warts), bleomycin, immunotherapy (SADBE, DPCP) |
| Molluscum contagiosum | MCV (poxvirus) | Dome-shaped, umbilicated, flesh-colored papules in children and immunocompromised | Watchful waiting (self-resolves 6-12 months); cryotherapy, curettage, cantharidin, topical imiquimod |
Skin Cancer
Basal Cell Carcinoma (BCC)
| Parameter | Detail |
|---|---|
| Origin | Basal layer of epidermis |
| Frequency | Most common skin cancer (80% of non-melanoma skin cancers) |
| Risk factors | UV exposure (cumulative), fair skin, age, arsenic, immunosuppression, genetic (Gorlin syndrome - PTCH1 mutation) |
| Subtypes | Nodular (most common, pearly nodule with telangiectasias, rolled borders), Superficial (flat, erythematous, scaling plaque), Morpheiform (sclerosing, scar-like, aggressive), Pigmented, Ulcerated (rodent ulcer) |
| Metastatic potential | Very low (<0.1%) |
| Treatment | Surgical excision (4 mm margins), Mohs micrographic surgery (high-risk areas: face, periocular, nose, ears), electrodesiccation and curettage (low-risk), topical imiquimod or 5-FU (superficial), radiation therapy (inoperable) |
Squamous Cell Carcinoma (SCC)
| Parameter | Detail |
|---|---|
| Origin | Keratinizing cells of epidermis |
| Frequency | Second most common skin cancer (16% of non-melanoma) |
| Risk factors | UV exposure (cumulative), fair skin, age, immunosuppression (organ transplant - 100x risk), chronic wounds/scars (Marjolin ulcer), HPV, arsenic, radiation |
| Precursor lesions | Actinic keratosis (AK), Bowen disease (SCC in situ) |
| Subtypes | Conventional, verrucous (low-grade), spindle cell, acantholytic, adenosquamous |
| Metastatic potential | 2-5% overall (higher for high-risk features: >2 cm, depth >2 mm, perineural invasion, poor differentiation, ear/lip location, immunosuppression) |
| Treatment | Surgical excision (4-6 mm margins for low-risk, wider for high-risk), Mohs micrographic surgery (high-risk), curettage and ED&C (low-risk), radiation (primary or adjuvant), cryotherapy (AK/Bowen), topical 5-FU/imiquimod (AK/Bowen) |
Melanoma
| Parameter | Detail |
|---|---|
| Origin | Melanocytes |
| Frequency | 4% of skin cancers but causes >75% of skin cancer deaths |
| Risk factors | UV exposure (intermittent, intense, blistering sunburns), fair skin (Fitzpatrick I-II), multiple nevi (>50), atypical (dysplastic) nevi, family history of melanoma, CDKN2A mutation, immunosuppression, personal history of melanoma |
| ABCDE criteria | Asymmetry, Border irregularity, Color variegation (multiple colors), Diameter >6 mm, Evolution (change over time) |
| Subtypes | Superficial spreading (70%, most common), Nodular (15-20%, aggressive, often symmetric), Lentigo maligna (5-10%, elderly, chronically sun-damaged skin), Acral lentiginous (2-5%, palms/soles/subungual, most common in darker skin types), Desmoplastic (neurotropic) |
Melanoma Staging and Treatment
| AJCC Stage | Breslow Thickness | Key Features | Treatment | 5-Year Survival |
|---|---|---|---|---|
| 0 (in situ) | In epidermis only | No invasion | Wide local excision (0.5-1 cm margins) | >99% |
| IA | <0.8 mm | No ulceration | WLE (1 cm margins) | 97-99% |
| IB | <0.8 mm with ulceration OR 0.8-1.0 mm | – | WLE + SLNB (consider) | 90-95% |
| IIA | 1.01-2.0 mm with ulceration OR 2.01-4.0 mm without ulceration | No nodal involvement | WLE + SLNB; consider adjuvant immunotherapy (if SLNB+) | 80-90% |
| IIB-IIC | >2.0 mm with ulceration OR >4.0 mm | No nodal involvement | WLE + SLNB; consider adjuvant immunotherapy (anti-PD-1) | 50-80% |
| III | Any thickness | Nodal involvement | WLE + lymph node dissection + adjuvant immunotherapy (nivolumab, pembrolizumab) or BRAF/MEKi (if BRAF mutant) | 25-60% |
| IV | Any | Distant metastases | Immunotherapy (anti-PD-1 +/- anti-CTLA-4), targeted therapy (BRAF/MEKi), clinical trials | 15-30% |
Skin Cancer Prevention
| Method | Recommendation |
|---|---|
| Sunscreen | SPF 30+ (broad-spectrum, water-resistant); 1 oz (shot glass) for full body; reapply every 2 hours; daily use |
| Protective clothing | Wide-brimmed hat, UV-blocking sunglasses, long sleeves/pants, UPF-rated clothing |
| Shade | Avoid sun 10 AM - 4 PM; seek shade when UV index >3 |
| Avoid tanning beds | Class 1 carcinogen (same category as tobacco) |
| Self-skin exams | Monthly; ABCD criteria; new or changing lesions require dermatology evaluation |
| Professional skin exams | Annually for average risk; more frequent for high-risk individuals |
| Vitamin D | Dietary sources and supplements preferred over UV exposure |