Medicine
Skin Barrier Function and Topical Corticosteroid Potency Selection
Quick fact
A steroid cream that is 'super-potent' on the face can cause irreversible skin thinning, but on the thick skin of the palms it might be barely effective.
Why this is interesting
Your skin looks like a wall, but sometimes it lets in medicine like a sieve. Why does the same cream work wonders on one person's eczema but fail on another's?
Read the full explanation
Understanding Skin Barrier Function and Topical Corticosteroid Potency Selection
Think of the skin as a brick-and-mortar wall. The bricks are dead skin cells (corneocytes) and the mortar is a lipid-rich matrix that keeps water in and irritants out. This outer layer, the stratum corneum, is the main barrier to anything applied on the skin. In healthy skin, this barrier is tight and prevents easy penetration. But in conditions like eczema or psoriasis, the barrier is often disrupted—the bricks loosen and the mortar cracks. This allows water to escape (increasing transepidermal water loss, or TEWL) and also allows topical drugs to penetrate more easily. This means that the same potency of corticosteroid can have a stronger effect on damaged skin than on intact skin. So when choosing a topical corticosteroid, doctors must consider not only the severity of the inflammation but also the state of the skin barrier. A very potent steroid might be necessary for a thick, lichenified plaque, but a mild one is safer for thin, delicate areas like the face.
A deeper explanation
The potency of a topical corticosteroid is determined by its ability to suppress inflammation, but its actual effect depends on how much of the drug reaches the living layers of the skin. The stratum corneum is the rate-limiting barrier: it is hydrophobic, so lipid-soluble drugs pass more easily, and it is thick, so molecules must be small enough to diffuse. When the barrier is compromised—for example, in atopic dermatitis—the skin becomes more permeable, allowing higher drug absorption. This is why a mid-potency steroid can cause adrenal suppression or skin atrophy if applied to widespread, damaged skin. Additionally, the vehicle (such as cream, ointment, or gel) influences drug release and occlusion; an ointment is more occlusive and enhances penetration compared to a cream. Therefore, selecting potency is a balance: it must be strong enough to treat the inflammation but not so strong that it causes local or systemic side effects. Clinicians classify steroids into seven potency groups (from class 1, super-potent, to class 7, very mild) and choose based on both disease severity and barrier integrity at the affected site. This understanding is critical for safe and effective prescribing.