What Is PPD in Sunscreen?
- premature ageing
- skin tanning
- skin cancer
An effective sunscreen has to offer protection against both UVA and UVB radiation.
Sun Protection Factor, commonly called SPF, tells us how long a sunscreen protects our skin from sunburn from UVB radiation.
PPD is a method used to rate the protection sunscreens offer against UVA radiation. PPD stands for persistent pigment darkening. Please note that PPD is not the only method used to rate protection against UVA radiation. It is one of the methods and is most commonly used in Asia and Europe.When unprotected skin is exposed to radiation from the sun, 2 types of tan can occur:
- immediate: occurs within one hour of exposure and can last up to 3 to 4 days. Caused mainly by UVA radiation.
- delayed: occurs a couple of days after the exposure. Caused by UVA and UVB radiation.
Both types of tan are related to melanin. Melanin is a pigment found in our skin. Melanin sits like a shield around the nucleus of cells, absorbs the UV light, and prevents UV from entering the nucleus and damaging it. The dark colour of melanin is what causes the tan.
When exposed to UV radiation, initially, existing melanin is redistributed to protect our skin cells from UV radiation. This causes the immediate tan. When the redistribution does not offer enough protection, more melanin starts getting generated. This causes the delayed tan. Tan is the after effect of the body's defence against UV light.
If we tan, it means the UV has already penetrated into the skin and the melanin is over-working and trying to protect our skin cells. If we apply the right sunscreen at the right intervals, we won't tan because sunscreen acts as the first layer of defence and UV can't bypass it. Melanin won't be so busy and so no tan.
Coming back to the rating method PPD, PPD measures the protection sunscreens offer from immediate tan. The immediate tan is caused by UVA radiation. So we can also say that PPD is a method to rate the protection from UVA radiation.
PPD of 10 means it will take around 10 times longer for the skin to tan immediately, compared to when it was unprotected. PPD of 20 means it will take around 20 times longer for the skin to tan, compared to when it was unprotected.