The Skin as a Drug Target
Skin structure and the barrier, topical vehicles and potency, and when dermatology goes systemic.
The Skin as a Drug Target: Why Topical Pharmacology Is Different
You can swallow a tablet and trust it will be absorbed. Smear the same drug on the skin and, most of the time, almost nothing gets in. The skin is not a passive wrapping — it is a chemical fortress, evolved over hundreds of millions of years to keep water in and the world out. That fortress is exactly what a topical drug must cross, and understanding its architecture is the difference between a cream that works and one that just sits on the surface. Every later dermatology chapter — steroids, retinoids, antifungals — is really a story about getting a molecule past this one wall.
Topical Vehicles & Potency: Ointment, Cream, Gel — and Why the Base Is a Drug Decision
In dermatology you never prescribe a molecule alone — you prescribe it dissolved in something. That something, the vehicle, decides how much of the drug ever reaches living skin. Choose an ointment and a steroid behaves as if it were a step stronger; choose a lotion and the same molecule barely gets in. The vehicle also decides whether the patient will actually use it: a greasy ointment on the face at 8 a.m. is a prescription that never gets filled twice. Getting the base right is not a cosmetic afterthought. It is half the pharmacology.
When Dermatology Goes Systemic: Escalation, Monitoring, and the Cost of Going Deep
The skin is the one organ a drug can reach without ever entering the bloodstream. That single fact defines dermatology's great advantage — you can lay medicine directly on the diseased tissue and spare the rest of the body almost entirely. So the first question in every skin disease is not "which drug?" but "can I stay on the surface?" Most of the time the answer is yes. But there is a line — drawn by how much skin is involved, where it sits, and whether the patient will actually use the cream — beyond which you must send the drug through the whole body to reach the skin. Crossing that line trades a rash for a blood-test schedule, and understanding the trade is the whole of dermatologic prescribing.
