The key to identifying your SPF is determining your skin type. Here are the six main skin types.
Do You KNow Your Skin Type?
Always burns easily, never tans, extremely sun sensitive. Includes red heads, freckle faced individuals.
Burns easily, tans minimally, also sun sensitive. Includes fair skinned, fair haired people. Many Northern Europeans fall into this group.
Sometimes burns, tans gradually to light brown, some sun sensitivity. Common among darker haired Caucasians.
Burns minimally, tans to moderate brown, and virtually no sun sensitivity.
Rarely burns, tans well, sun-insensitive skin. Includes Middle Eastern People, some Hispanics, some African Americans, and some native Americans.
Never burns, deeply pigmented, sun-insensitive skin.
We have already discussed the six different skin types and the impact of UV rays on each. There are other natural factors that can increase or decrease this impact:
Geographic location (closer to equator means more sun)
Time of year
Time of day
Amount of tanning already achieved
Length of time spent in the sun
This last factor brings us to a review of sun care products. The SPF classification, or number, indicates the level of protection against UVB rays (the cause of sunburn) and helps determine the amount of time a person can stay in the sun without getting a burn.
The higher the SPF number, the stronger the protection and the longer the user can stay out. The FDA classifies sunscreens as those products with SPFs of 2-14; and SPFs of 15 and higher. The following table correlates SPF rating to the percent of UVB rays screened/blocked:
For example, let's assume you're at sea level and have no prior tan. From personal experience, you know that after about 15 minutes of sun, you start to burn.
If you plan to be in the sun for an hour, you need protection equivalent to the remaining 45 minutes, so you would use SPF 4 which screens out 75% of UVB rays or 45 minutes worth (75% x 60 minutes = 45 minutes of block).
The SPF to be used is determined by dividing the time a person will be in the sun by the amount of time it takes to start burning (60 minutes divided by 15 minutes = SPF 4).
So with SPF 4, after an hour of sun, your skin has received only 25% of the UVB rays. Any more sun and you'll begin to burn with this level of SPF. To get more protection, start with a higher SPF. An SPF of 8, for example, protects for two hours (87.5% x 120 minutes = 105 minutes of block plus 15 minutes before you burn).
Another way to calculate sun time is to multiply the SPF number by the "time it takes to burn". In the previous illustration, and SPF of 15 times 15 minutes to burn equals 225 minutes (3 3/4 hours) protection. Add to this the 15 minutes it takes to burn, and you have 240 minutes (4 hours) before you start to burn.
It's important to note that you cannot extend protection by reapplying the same level of SPF. A person using SPF 4 can take one hour of sunning. If they plan to stay two hours, they must apply an SPF 8 or higher. The reason for this is that the skin has already received an hour of UVB rays.
SPF protection is not cumulative; two applications of SPF 4 can't give the equivalent of an SPF 8, nor does adding SPF 4 to SPF 8 yield the equivalent of SPF 12.
According to a recent Gallup study, only 54% of adults used any sun care products. Only 43% used a product with an SPF of 6 or above. Although 81 % of teenagers spend most weekends in the sun, during those weekends, only 9% regularly use sunscreen. 58% use none at all.
Education plays a role in the use of sun care products as the more educated have a greater awareness of health care issues. But there still exists a significant amount of confusion. Most people do not understand how to select the right SPF nor how much to apply.
As mentioned earlier, reflection off the water can increase sun concentration by 40%. Said another way, burning will occur in 9 minutes, not 15. So, the sailing enthusiast would need to use an SPF 8 to get an hour's protection (60 minutes divided by 9 = 6.6).