Minimum Erythema Dose (MED) & UV Therapy: Simplified

The minimum erythema dose (MED) refers to the smallest amount of UV radiation required to cause visible skin redness (erythema) within 24–48 hours. It is crucial for guiding safe UV therapy in treating conditions like psoriasis, vitiligo, and eczema. Clinicians measure MED by exposing small areas of skin to controlled UV radiation (e.g., narrowband UVB at 311 nm), with visual assessment remaining the gold standard. MED varies significantly by skin type: fair skin (Fitzpatrick Type I) typically needs 20–50 mJ/cm², while darker skin (Type VI) may require over 500 mJ/cm². This personalized threshold helps balance therapeutic effects and safety.

Factors influencing MED include skin pigmentation (darker skin absorbs more UV, demanding higher doses), ambient light (dim light enhances erythema visibility), and skin health/age (damaged or aged skin has a lower MED). To standardize MED reporting across studies, the standard erythema dose (SED) was proposed—defined as 100 mJ/cm² of UVB—enabling cross-study comparisons.

In UV therapy, low-dose UVB (20% of MED) for vitiligo has shown efficacy: 63.6% of patients achieved over 25% repigmentation after 6 months, with fewer side effects like blistering. Initial doses start at 10–20% of MED; if no erythema occurs, increase by 10–20% every 2–4 sessions, and reduce by 20–50% if erythema persists over 72 hours. Current challenges include subjective MED assessment and biological variability; future advances involve wearable UV dosimeters and targeted 308 nm excimer lasers (related products available at https://zjkcshop.com/collections/308nm-uvb-light).