Skin care: how long does sunscreen last?

At most 2 hours: Although the spf rating of a sunscreen tells you how effective it is during use, it is important to reapply frequently and in adequate amount. Sunscreen should be reapplied every 2 hours to maintain efficacy, as factors such as sweating, water exposure, and physical removal can decrease its effect and lead to burns and skin cancer risk.

Varies by type: This will vary according to the product as well as the activities of the individual ( sweating, exercise, bathing/swimming). Appropriate instructions are usually provided with the product