what spf means

SPF stands for Sun Protection Factor, and it is a measure of how much solar energy (UV radiation) is required to produce sunburn on protected skin (i.e., in the presence of sunscreen) relative to the amount of solar energy required to produce sunburn on unprotected skin. As the SPF value increases, sunburn protection increases. However, it is important to note that SPF is not directly related to time of solar exposure but to the amount of solar exposure. For example, if your skin would normally burn after 10 minutes in the sun, applying an SPF 15 sunscreen would allow you to stay in the sun without burning for approximately 150 minutes (a factor of 15 times longer) . This is a rough estimate that depends on skin type, intensity of sunlight, and amount of sunscreen used. Most dermatologists recommend using SPF 30 or higher, and much higher SPFs dont provide that much more protection. It is also important to note that SPF measures sunscreen protection from UVB rays only, which cause sunburn and contribute to skin cancer, and does not measure sunscreen protection from UVA rays, which are also damaging and dangerous to your skin. Therefore, it is recommended to look for the words "broad spectrum" on a products label, which means it has ingredients that can protect you from UVA as well as UVB rays.