Updated: Oct 13, 2022
While everyone needs a little sun exposure to get their annual vitamin D fix, too much sun can be dangerous. That’s where sunscreens come into play.
Choosing and using sunscreen is critical for shielding you from the sun’s dangerous ultraviolet rays. Here’s an explanation of SPF (Sun Protection Factor) ratings, the meaning behind all those numbers, and ultraviolet radiation.
SPF and Sunscreen Ratings. A sunscreen’s SPF, or “sun protection factor,” refers to its ability to shield from the sun’s ultraviolet rays. It is a measure of the time it would take for a person to start getting red if he or she was not wearing sunscreen.
In general, it takes about 10 to 20 minutes without sunscreen for a person’s skin to start burning. An SPF 15 product would prevent skin from burning for 15 times longer – so about 150 to 300 minutes, or about 2.5 to five hours. However, that doesn’t mean you’re fully protected for that five hours. Dermatologists highly recommend reapplying sunscreen every two to four hours, as sunscreen can rub off or get washed off in the water.
For many, such numbers can get confusing. It is a common misunderstanding that “SPF 30” is twice as good as “SPF 15”. But that’s not how it works.
A sunscreen with an SPF 15 blocks about 94 percent of the sun’s dangerous rays. SPF 30 products block about 97 percent of such rays and SPF 45 sunscreen shields against about 98 percent of rays. There’s really no need to go any higher.
Protection Grade of UVA rays
Have you ever noticed a PA+++ rating in the sunscreens along with SPF level? Some people might have just ignored while, some confused. SPF indicates the level of protection from UVB rays while PA indicates the level of protection from UVA rays.
PA simply means Protection Grade of UVA rays, which is used to measure the SPF of a sunscreen. This Japanese measurement ranking which is now widely used is based on the Persistent Pigment Darkening (PPD) reaction reading at 2-4 hours of sun exposure. The protective grade of sunscreen is often leveled as PA+, PA++, PA+++ with the more plus sign the more protection from UVA rays.
According to the Japan Cosmetic Industry Association UVA protection factor for each grading of PA are listed below:
PA+ means the sunscreen can provide UVA protection with a factor of Persistent Pigment Darkening (PPD) between two to four. It can provide protection against medium UV radiation.
Sunscreen labeled with PA++ can provide moderate protection against UVA rays with a factor of PPD between four and eight. It is ideal for normal skin individuals exposed to medium UV radiation.
PA+++ is designed for normal skin that exposes to extreme UV radiation. It provides good UVA protection with a factor of PPD of more than 8. It is the highest grade of UVA protection currently available.
Although many products in the market are labeled as “broad-spectrum” they do not give adequate protection against UVA rays. UVA protection is better achieved by products containing zinc oxide. UVB just causes sunburn while UVA causes permanent aging of the skin and even increases the risk of skin cancer. So it is important to strictly use sunscreen that protects from both UVA and UVB radiation.
To achieve maximum protection from both UVA and UVB, always look for a broad-spectrum sunscreen that contains zinc oxide and titanium dioxide. Other ingredients to look for are oxybenzone, avobenzone, and Mexoryl. Don’t forget to apply sunscreen for at least 20 minutes before going out. Always use sunscreen throughout the year, not just during the summer months.
Adapted from: http://www.ibtimes.com/what-do-sunscreen-numbers-mean-spf-ratings-brands-uv-rays-explained-1978100 & http://www.dermatalk.com/blogs/skincare/spf-and-pa-rating-in-sunscreen-what-does-it-indicate