Clinical studies in dermatology require a post-treatment observation phase to define the impact of the intervention on the natural history of the complaint.

The use of a post-treatment period of observation or "regression phase" is common in pharmaceutical and cosmetic clinical dermatology studies. Regression phases can be incorporated into a variety of study designs, ranging from simple post-treatment observation for a defined period, as has been used for moisturizers, antidandruff formulations, and treatments for acne, to more complex randomized intermittent-treatment designs, as used in studies of psoriasis pharmacotherapies. Extensive information can be derived from a regression phase. Notably, it can provide useful data on the persistence of effect and time to relapse after treatment cessation, which are particularly relevant to skin conditions in which consumer or patient adherence to treatment is suboptimal. By incorporating a regression phase, a clinical study can more closely reflect "real-world" behavior, e.g., the switching by consumers from antidandruff to beauty shampoos. The regression phase can also help to differentiate between products that show similar effectiveness during the treatment phase, and monitoring post-treatment physiological end points can provide valuable evidence on the safety and mechanism of action of the therapy.