Minimal Erythema Dose (MED)

The minimal erythema dose (MED) is the lowest dose of light energy that produces a just-perceptible redness (erythema) in a given person’s skin. Originating in UV phototherapy, the concept is a practical way to quantify how a specific individual’s skin responds to light.

The principle carries directly into laser and IPL safety. Because skin response varies with Fitzpatrick type, recent sun exposure and medication, the dose that is effective and safe for one client may burn another. This is the rationale behind the test patch: treating a small, discreet area first and observing the reaction lets the operator find a fluence that gives a controlled response well below a harmful one before treating the full area. Thinking in terms of MED reframes ‘turning up the energy’ as finding each client’s individual threshold.

For clinics, respecting the MED principle through test patching is a simple, powerful way to prevent adverse events and demonstrate professional rigour.