Currently, sunscreens are measured by their sun protection factor (SPF) which is only a measure of UVB protection. Make sure your sunscreen says it is broad-spectrum and also protects against harmful UVA rays.
Statistically, most people only use about 1/3 of the recommended amount of sunscreen. For example, if you were to apply an SPF 30 sunscreen to your skin, the actual volume of sunscreen that is typically used is only equal to an SPF 10.
So it is important to realize that with sunscreen, the number on the label is not necessarily the amount of protection you�re actually receiving. Using a higher number SPF sunscreen helps increase your chances of getting enough sun protection.
*Remember that water, humidity, and sweating decrease the effectiveness of sunscreen and numerous reapplications are necessary.