25 Dermatology Quick FAQs
Concise answers to the 25 questions most often asked in clinic and online forums. For deeper coverage of each topic, follow the linked articles.
Q1. Why apply retinoids only at night?
Retinoids (Adapalene, Tretinoin, Tazarotene, Trifarotene) are UV-degraded and photosensitizing. Apply at night, wash off in morning, and use sunscreen daily. New-generation retinoids like Adapalene are more photostable but bedtime application remains standard.
Q2. Can topical steroids be used long-term? Will they thin the skin?
Used correctly — yes, safely. Atrophy / striae / telangiectasia only occur with prolonged inappropriate use. Match potency to body site:
- Face / eyelids / genitals / folds: Class V-VII (mild)
- Trunk / limbs: Class III-IV (mid-strength)
- Palms / soles: Class I-II (super-potent)
Strategy: acute phase daily for 2 weeks, then "weekend therapy" (twice-weekly) maintenance.
Q3. Tacrolimus vs Pimecrolimus — what's the difference?
Both are calcineurin inhibitors (TCIs). Tacrolimus 0.03% / 0.1% is stronger; Pimecrolimus 1% is gentler. Used for face, eyelids, folds where steroids carry atrophy risk. Initial burning common (resolves in days). FDA black-box warning for theoretical lymphoma risk has been challenged by 20-year safety data — short-term to several-month use is safe.
Q4. How does Vitamin C serum stack with retinoids?
L-ascorbic acid works at pH 3.5, retinoids at pH 5-6. Direct mixing creates pH conflict, mutually inactivating. Strategy: Vitamin C in morning + sunscreen, retinoid at night. If layering same time, allow 30 minutes between.
Q5. AHA / BHA / PHA — which to choose?
| Acid | Examples | Best for |
|---|---|---|
| AHA (water-soluble) | Glycolic, lactic, mandelic | Brightening, mild texture |
| BHA (oil-soluble) | Salicylic acid | Acne / blackheads (penetrates pores) |
| PHA (gentle, large molecule) | Gluconolactone, lactobionic acid | Sensitive skin |
Q6. How much sunscreen to apply?
Face: 1.25 mL (~½ teaspoon). Most people apply only 1/3 the lab-tested amount, getting only ~⅓ the SPF. "Two-finger-length" rule: a strip from index-finger tip to base of palm covers face + neck. Reapply every 2 hours when outdoors.
Q7. Can I get pregnant on / right after isotretinoin?
Isotretinoin is severely teratogenic (Category X). Pregnancy ban: throughout treatment AND 1 month after stopping. Use 2 simultaneous contraceptive methods. Pregnancy test at baseline + monthly during treatment + 1 month after.
Q8. What's the order: cleanser → toner → serum → moisturizer?
Standard order (thin to thick): cleanser → toner / essence → serum (treatment) → moisturizer / lotion → sunscreen (morning only). Multi-layering "K-beauty 7-step" isn't necessary; 3-4 essential steps suffice for most skin.
Q9. Why does skin "purge" when starting retinoids? Should I stop?
"Retinoid purge" = retinoids accelerate cell turnover, pushing existing micro-comedones to surface as acne flares. Usually 4-8 weeks, then improvement begins. Persist with reduced frequency (every 2-3 nights) and good moisturization. Resolves by week 8-12 typically.
Q10. Doxycycline vs Minocycline — which?
Both tetracyclines effective for acne / rosacea. Doxycycline preferred (less risk of vertigo, hyperpigmentation). Sub-antibiotic dose 40 mg modified-release for rosacea has anti-inflammatory effect without resistance. Avoid in < 8 yo (teeth staining) and pregnancy.
Q11. What blood tests does isotretinoin need?
Baseline: CBC, AST/ALT, lipid panel (cholesterol, triglycerides), pregnancy test (women). Re-check at 1 month, then every 2-3 months. Recent evidence supports less frequent monitoring in healthy young adults without comorbidities.
Q12. Spironolactone for adult female acne?
Off-label but well-supported. 50-200 mg/day blocks androgen receptors, reduces sebum. Watch for hyperkalemia (renal insufficiency, ACE-I/ARB co-use), spotting, breast tenderness. Avoid pregnancy. Often combined with topical retinoid + COCP.
Q13. NB-UVB vs PUVA?
NB-UVB (311 nm narrowband) is current first-line: safer, no oral psoralen needed, less skin cancer risk. PUVA (psoralen + UVA) more potent but requires oral drug, sun-avoidance for 12-24h, higher long-term skin cancer risk.
Q14. Can I take biologics during pregnancy?
Most biologics (Adalimumab, Certolizumab) cross placenta; Certolizumab least crosses. Decisions individualized per disease severity vs theoretical risk. Discuss with rheumatologist / dermatologist + maternal-fetal medicine.
Q15. Tea tree oil for acne?
5-15% tea tree oil shows modest efficacy in mild-moderate acne (slower than benzoyl peroxide but better tolerated by sensitive skin). Allergic contact dermatitis possible — patch test first.
Q16. Why does eczema flare in winter?
Cold + low humidity + indoor heating → skin barrier dehydration → TEWL increases → barrier breakdown → eczema flare. Strategy: humidifier (40-60%), shorter / cooler showers, ceramide moisturizer immediately after bath, proactive twice-weekly TCI on prone areas.
Q17. Hyaluronic acid — does the molecular weight matter?
High MW (> 1,000 kDa) stays on surface, occlusive moisture. Low MW (< 50 kDa) penetrates a bit deeper. Multi-MW formulas combine both. The benefit is real but modest; ceramides are arguably more important for barrier repair.
Q18. Microneedling: home roller vs in-clinic?
Home rollers (0.2-0.5 mm) only enhance product penetration. Clinical microneedling (1.0-2.5 mm + RF) reaches dermis for collagen induction — works for atrophic acne scars, fine lines. Sterility / depth control / post-care differ enormously.
Q19. Botox for facial flushing / rosacea?
"Microbotox" (highly diluted intradermal botulinum toxin) reduces sebum, sweat, vasoreactivity in some refractory cases. Off-label, lasts 3-6 months. Not first-line; consider after standard topical / laser fail.
Q20. Vitamin D and hair loss / acne / eczema?
Mixed evidence. Replete deficiency if < 30 ng/mL — may modestly help hair shedding in TE/AGA. No solid acne / eczema benefit beyond replete deficiency. Avoid mega-dosing.
Q21. Are stretch marks treatable?
Best results within first year (red striae rubra) using PDL or fractional laser. Mature white striae (alba) much harder. Topical tretinoin + microneedling has modest effect. Manage expectations: 30-50% improvement realistic.
Q22. Hyperpigmentation vs Melasma — same treatment?
No. Post-inflammatory hyperpigmentation (PIH) often clears with sunscreen + tretinoin / azelaic / hydroquinone in 3-6 months. Melasma is chronic, hormone-influenced, easily rebounds — needs strict sun protection, Tri-Luma or tranexamic acid, and very cautious laser (low energy only).
Q23. Atopic dermatitis food allergy: should I cut everything?
No, not without confirmation. Blind elimination causes nutritional deficits with rare benefit. Only avoid food where there's a clear temporal relationship (eat → flare within 30 min - 2 h, every time). Consider oral food challenge under specialist supervision.
Q24. Why "moisturize within 3 minutes after shower"?
Skin barrier is most receptive to moisturizer when slightly damp. Beyond 3-5 minutes, water loss creates further dehydration. Pat skin dry (don't rub), apply moisturizer immediately. This single habit dramatically improves dry / atopic skin.
Q25. Why visit a dermatologist instead of self-treating?
Many "skin problems" look similar but need different treatments. Misdiagnosis costs months and worsens disease (e.g., applying retinoids to rosacea, or steroids to tinea). A 5-minute dermatologist visit + correct prescription often resolves what 3 months of trial-and-error didn't.