What is SPF? How SPF is Measured?
What is SPF?
SPF stands for Sun Protection Factor. SPF (Sun Protection Factor) is a multiplication factor you can use to determine how long you can stay out in the sun before getting a sunburn. It is mainly a measure of UVB protection and ranges from 1 to 45 or above, however SPF does not predict UVA protection.
UVB (Ultraviolet B radiation) causes skin reddening and sunburn, and plays a key role in the development of skin cancer and a contributory role in tanning.
UVA (Ultraviolet A radiation) penetrates the skin more deeply than UVB, plays a major part in skin aging and wrinkling. UVA contributes to the initiate development of skin cancers.
How SPF is Measured?
One easy way to understand how SPF is measured: let say normally you can stay out in the sun for 20 minutes before getting burn, a sunscreen with an SPF of 5 will let you stay out 5 times as long (100 minutes or 1 hour and 40 minutes) before you getting burn.
The “protectiveness” of clothing can also be measured by SPF. The following are SPF’s of various types of clothing:
Nylon Stockings – SPF 2
Hats – SPF 3-6
Summer-weight clothing – SPF 6.5
Sun-protective clothing – up to SPF 30
|
UV Index |
Description |
Media Graphic Color |
Recommended Protection |
|
0–2 |
No danger to the average person |
Green |
Wear sunglasses on bright days; use sunscreen if there is snow on the ground, which reflects UV radiation, or if you have particularly fair skin. |
|
3–5 |
Little risk of harm from unprotected sun exposure |
Yellow |
Wear sunglasses and use SPF 30+ sunscreen, cover the body with clothing and a hat, and seek shade around midday when the sun is most intense. |
|
6–7 |
High risk of harm from unprotected sun exposure |
Orange |
Wear sunglasses and use SPF 30+ sunscreen, cover the body with sun protective clothing and a wide-brim hat, and reduce time in the sun from two hours before to three hours after solar noon (roughly 11:00 to 16:00 during summer in zones that observe daylight saving time). |
|
8–10 |
Very high risk of harm from unprotected sun exposure |
Red |
Wear SPF 30+ sunscreen, a shirt, sunglasses, and a hat. Do not stay out in the sun for too long. |
|
11+ |
Extreme risk of harm from unprotected sun exposure |
Violet |
Take all precautions, including: wear sunglasses and use SPF 30+ sunscreen, cover the body with a long-sleeve shirt and trousers, wear a very broad hat, and avoid the sun from two hours before to three hours after solar noon (roughly 11:00 to 16:00 during summer in zones that observe daylight saving time). |
