Be Sun Safe
How Much Sunscreen
The ideal amount of protection involves applying one full ounce (the volume of a shot glass) over your entire body. Note that rays can penetrate some regular clothing, so apply all over–before you get into your swimsuit. Chemical sunscreens need to be applied 30 minutes before sun exposure to allow the ingredients to fully penetrate the skin.
When To Reapply Sunscreen
Reapplying sunscreen is as important as putting it on in the first place. Reapply that full ounce of product every two hours as well as immediately after swimming, toweling off or sweating a great deal.
The Skin Cancer Foundation points out that for a full day at the beach, you’ll need to allot about half of an 8-ounce bottle of sunscreen for each person.
Sunscreens may be labeled “water-resistant,” in which case the product must specify whether testing showed it lasts for 40 or 80 minutes of swimming or sweating.
Resource: American Academy of Dermatology