15.6 Common Skin Conditions: Eczema, Contact Dermatitis, Psoriasis, Tinea, Vitiligo, Skin Lesions & Hidradenitis
Key Takeaways
Atopic dermatitis is treated with daily emollients plus topical corticosteroids for flares, with topical calcineurin inhibitors for the face and skin folds.
Allergic contact dermatitis (nickel, fragrances, poison ivy) is a type IV reaction; extensive cases need a systemic steroid taper of about 2–3 weeks, because short dose packs cause rebound.
Tinea shows an annular scaling border with central clearing and hyphae on KOH; topical azoles or terbinafine treat body infections, while scalp and nail infections need oral therapy.
Methotrexate and acitretin for psoriasis are teratogens; acitretin requires avoiding pregnancy for 3 years after stopping.
Basal cell carcinoma, the most common skin cancer, is a pearly papule with rolled borders and telangiectasias; the USPSTF finds insufficient evidence for routine clinician skin cancer screening but recommends sun-protection counseling for fair-skinned people aged 6 months to 24 years.
Atopic Dermatitis (Eczema)
A chronic, relapsing, intensely itchy dermatitis tied to skin barrier defects (filaggrin) and type 2 inflammation, often with asthma and allergic rhinitis. Adults typically have flexural, hand, eyelid, and neck involvement with lichenification.
- Foundation: Fragrance-free emollients at least daily (after bathing), lukewarm short showers, and gentle cleansers.
- Flares: Topical corticosteroids matched to site (low potency for the face, groin, and folds; medium to high potency for the trunk and extremities for limited courses).
- Steroid-sparing therapy: Topical calcineurin inhibitors (tacrolimus, pimecrolimus) for the face and folds; crisaborole and topical JAK inhibitors for selected patients.
- Moderate to severe disease: Phototherapy or dupilumab; oral JAK inhibitors carry boxed warnings.
- Pregnancy: Emollients and low- to mid-potency topical steroids are preferred; narrowband UVB is safe.
Contact Dermatitis
| Feature | Irritant Contact Dermatitis | Allergic Contact Dermatitis |
|---|---|---|
| Mechanism | Direct damage (soaps, water, solvents); no sensitization | Type IV delayed hypersensitivity after sensitization |
| Common causes | Frequent handwashing, wet work, diapers, incontinence | Nickel (jewelry), fragrances, preservatives, hair dye, poison ivy/oak (urushiol), topical antibiotics (neomycin) |
| Appearance | Burning, dryness, fissuring at the contact site | Itching, vesicles, sharp borders or linear streaks matching the exposure |
| Diagnosis | History | Patch testing for recurrent or unclear cases |
Treatment: Avoid the trigger, use barrier protection and emollients, and apply topical steroids. Extensive poison ivy or facial involvement needs oral prednisone tapered over about 2–3 weeks; a 5–6-day dose pack often causes rebound. Vulvar contact dermatitis from pads, wipes, douches, or topical anesthetics (benzocaine) is a common gynecologic presentation.
Psoriasis
An immune-mediated disease (IL-17 and IL-23 pathways) with well-demarcated, erythematous plaques with silvery scale on the extensor elbows and knees, scalp, gluteal cleft, and nails (pitting, onycholysis). It shows the Koebner phenomenon (lesions at sites of trauma). About 30% develop psoriatic arthritis, and patients have higher rates of cardiovascular disease, metabolic syndrome, and depression.
- Mild disease: Topical corticosteroids, vitamin D analogs (calcipotriene), and newer nonsteroidal creams (tapinarof, roflumilast).
- Moderate to severe disease: Narrowband UVB phototherapy; systemic agents including methotrexate (teratogen; stop at least 3 months before conception), acitretin (highly teratogenic; avoid pregnancy for 3 years after stopping), apremilast, and biologics (TNF, IL-17, and IL-23 inhibitors).
- Pregnancy: Psoriasis often improves; certolizumab pegol has minimal placental transfer and is preferred when a biologic is needed. Generalized pustular psoriasis of pregnancy is an emergency.
Superficial Fungal Infections (Tinea)
Diagnosis: A KOH preparation shows branching hyphae. Applying topical steroids to tinea causes "tinea incognito," a spreading, atypical rash.
| Type | Presentation | Treatment |
|---|---|---|
| Tinea corporis | Annular plaque with a scaling, raised border and central clearing | Topical azole or terbinafine for 2–4 weeks |
| Tinea cruris | Groin rash that spares the scrotum or vulva and labia; candidal intertrigo involves them, with satellite lesions | Topical antifungal; keep the area dry |
| Tinea pedis | Interdigital maceration or a "moccasin" scaling pattern | Topical antifungal; treat to prevent cellulitis |
| Tinea capitis | Scaly patches with hair loss; mostly children | Oral terbinafine or griseofulvin |
| Onychomycosis | Thick, discolored, crumbling nails | Confirm by culture or KOH; oral terbinafine for 12 weeks (toenails); check liver enzymes |
| Tinea (pityriasis) versicolor | Hypo- or hyperpigmented, finely scaling macules on the trunk; KOH shows "spaghetti and meatballs" (Malassezia) | Selenium sulfide or ketoconazole shampoo applied to the skin; pigment takes months to normalize |
Oral azoles (fluconazole, itraconazole) have many drug interactions and are avoided in pregnancy.
Vitiligo
An autoimmune loss of melanocytes producing sharply demarcated depigmented macules, often around the eyes, mouth, hands, and genitals, accentuated under Wood's lamp. It is associated with autoimmune thyroid disease (check TSH), type 1 diabetes, pernicious anemia, and alopecia areata. Treatment includes topical corticosteroids, topical calcineurin inhibitors, topical ruxolitinib (FDA-approved in 2022 for nonsegmental vitiligo in patients 12 and older), and narrowband UVB, plus sun protection and attention to its psychosocial impact.
Benign, Premalignant, and Malignant Lesions
| Lesion | Description | Management |
|---|---|---|
| Seborrheic keratosis | Waxy, "stuck-on," brown papules | Benign; remove if irritated; a sudden eruption of many lesions (Leser-Trélat sign) may signal internal cancer |
| Dermatofibroma | Firm papule that dimples when pinched | Benign |
| Cherry angioma | Small bright red papules | Benign |
| Actinic keratosis | Rough, scaly patches on sun-exposed skin | Premalignant (can become SCC); cryotherapy, topical 5-fluorouracil or imiquimod |
| Basal cell carcinoma | Pearly papule with rolled borders and telangiectasias, may ulcerate ("rodent ulcer") | Most common skin cancer; rarely metastasizes; shave or punch biopsy, then excision or Mohs surgery |
| Squamous cell carcinoma | Scaly, crusted, or ulcerated nodule on sun-exposed skin; higher risk with immunosuppression and HPV | Can metastasize; biopsy and excision |
| Melanoma | ABCDE changes or an "ugly duckling" lesion (see the acne, rosacea, and pregnancy dermatoses section) | Excisional biopsy for Breslow depth |
USPSTF: Evidence is insufficient (I statement, 2023) for routine clinician skin examination for skin cancer in asymptomatic adults, but the USPSTF recommends sun-protection counseling for fair-skinned people aged 6 months to 24 years (grade B) and selectively for older adults. Counsel on broad-spectrum SPF 30 or higher, protective clothing, and avoiding tanning beds.
Hidradenitis Suppurativa
A chronic inflammatory disease of hair follicles in the axillae, groin, inframammary folds, buttocks, and vulva, with recurrent painful nodules, abscesses, sinus tracts, and scarring. It is about three times more common in women and linked to obesity and smoking. It is often misdiagnosed as recurrent boils or Bartholin abscesses. Management includes smoking cessation and weight loss, topical clindamycin, oral tetracyclines (avoided in pregnancy), spironolactone or combined pills for hormonal flares, biologics (adalimumab, secukinumab, bimekizumab), and surgery for sinus tracts.
A 34-year-old has an itchy, red, scaling rash in both groin folds that extends onto the upper inner thighs. The vulva and labia are spared, and the advancing border is raised and scaly with central clearing. She has been applying an over-the-counter hydrocortisone cream, and the rash is spreading. What is the most appropriate treatment?
Increase to a high-potency topical corticosteroid twice daily for 4 weeks to control inflammation.
Prescribe oral fluconazole 150 mg weekly for 6 months for presumed recurrent candidiasis.
Prescribe a 5-day burst of oral prednisone and continue the hydrocortisone cream.
Stop the steroid and use a topical azole or terbinafine for 2–4 weeks after KOH confirmation.
A 29-year-old with severe plaque psoriasis asks about acitretin because she has heard it works well. She hopes to become pregnant in the next 2 years. What is the most important counseling point?
Acitretin is preferred in women planning pregnancy because it clears from the body within days.
Acitretin is safe as long as she stops taking it as soon as a pregnancy test turns positive.
Acitretin requires avoiding pregnancy for 3 years after stopping, so it does not fit her plans.
Acitretin is only a concern for male partners, who must avoid conception for 3 months.
A 26-year-old has a widespread, intensely itchy, vesicular rash in linear streaks on her arms and legs 2 days after clearing brush. It covers about 30% of her body surface, including her face. What is the most appropriate treatment?
Oral prednisone tapered over 2–3 weeks, plus avoidance and skin washing
A short 5-day methylprednisolone dose pack, stopped without a taper
Topical neomycin ointment applied to all affected areas twice daily
Oral terbinafine 250 mg daily for 2 weeks for a dermatophyte infection
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