Bioderma Photoderm Photerpès SPF50+ Lip Stick is a sunscreen stick that helps to prevent the reactivation of the cold sore (herpes) virus. Cold sore blisters are often aggravated by direct exposure to solar radiation and the virus can be reactivated by these radiations, so solar protection is key to preventing herpes from being active. This lip stick has an anti-UVB protection index of SPF50+ and anti-UVA index of 24. Besides these sunscreen abilities, the main ingredient of this product is Glycyrrhizic acid which has been proven to inhibit virus activation and therefore helps to prevent cold sore bursts.