Red and blue light is a physical treatment method commonly used in dermatology, and the specific number of treatments needs to be determined by the damage to the skin. Red and blue light treatment uses the special wavelengths of red and blue light to play an anti-inflammatory and sterilizing role, and is mainly used clinically to treat acne, allergic dermatitis, hormone-dependent dermatitis and other dermatological diseases. Under normal circumstances, after 3-5 red and blue light treatments, the skin problems caused by acne as well as dermatitis can be significantly improved. In the case of moderate acne or more severe skin damage, the number of treatments needs to be increased appropriately to produce results. During the treatment period, attention should be paid to sun protection measures, such as applying sunscreen, wearing a sun hat or umbrella, and hydration to prevent dry and dehydrated skin after blue light treatment, which can lead to the formation of pigmentation or aggravation of pigmentation.