When spending time out of doors in summer, certain rules of behavior need to be observed. Environmental factors such as, for example, water, the beach and the midday sun all have a major influence on the UV radiation burden to which people may be subjected. In addition, the sun's rays can interact with certain medications, alcohol and drugs, as also cosmetics, and trigger pathological skin reactions. A permanently sun-damaged skin is not only very difficult to treat, but is also frequently associated with malignant changes. Moderate exposure to the sun after prior gradual acclimatization is to be recommended. Patients with increased photosensitivity require special photoprotective agents.