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).