Sunscreen-containing shampoos, conditioners, and hair sprays are now available. Apply initially 15 to 30 minutes before venturing outdoors. Reapply every two hours or so even on overcast days and each time after exercise or swimming. Choose a waterproof or water resistant formula even if activities don't include swimming. Waterproof formulas last for about 40 minutes in the water, whereas water-resistant formulas last half as long.
Insect repellents reduce sunscreen SPFs by up to one-third.
Use higher SPFs and very liberal application when applying both. Possible Hazards of Sunscreens, Sun Avoidance, or Both When used generously and appropriately, sunscreen products and sun avoidance help reduce the severity of many aging skin disorders, including squamous cell cancers. There are certain concerns, however. Increased Risk or No Protection for Basal Cell and Melanoma Cancers with Sunscreen Use . Although sunscreens help prevent squamous cell carcinoma and other skin disorders, sunscreens to not appear to provide protection against melanoma and some basal cell cancers.