How long will sunblock with an SPF of 20 provide protection?

The answer indicating that sunblock with an SPF of 20 provides approximately 400 minutes of protection is based on a general understanding of SPF, which stands for Sun Protection Factor. The SPF rating indicates how long a product can protect you from UV rays compared to unprotected skin.

To determine the protection duration, you can use the formula: multiply the SPF number by the number of minutes it takes for your skin to start burning without any protection. For example, if it takes 20 minutes to get a sunburn without any sunscreen, using a sunscreen with SPF 20 can theoretically extend that time.

Thus, with SPF 20, protection would last for 20 minutes multiplied by 20, resulting in 400 minutes of protection. This calculation assumes proper application and consistent reapplication, particularly if swimming or sweating, which can reduce effectiveness.

Understanding this concept allows for better practical application of sunblock, ensuring adequate protection during outdoor activities.