What does SPF 30 mean and how long does it protect against the sun?

Sunscreen is a product that many people have and it is also a must-have sunscreen product in summer. So what does sunscreen SPF30 mean? How long does spf30 sunscreen last?

What does SPF30 mean in sunscreen?

Most sunscreen products are labeled with SPF or PA. SPF (Sun Protection Factor) is a numerical value that shows the sunscreen effect in preventing UVB damage, while PA (Protection UVA) is an indicator of the extent to which UVA is protected. SPF is simply a sun protection factor.

The SPF value determines the ability of sunscreen to fight UVB. The higher the SPF value, the stronger the ability to protect against UVB. The calculation method is: assuming that the intensity of ultraviolet rays will not change with time, a person without any sun protection measures will have his skin turn red after staying in the sun for 20 minutes. When he uses SPF15 sunscreen, it means that the time can be extended 15 times, that is, the skin will not turn red until 300 minutes later. Therefore, the calculation formula for SPF30 protection against UVB is: the time the skin is exposed to the sun and becomes red * the size of the SPF value (30) = the time the sunscreen is effective in protecting against UVB rays.

PA+++ refers to protection against ultraviolet rays UVA. The more +s there are, the stronger the ability to fight UVA. PA+ can protect against UVA for 2 hours. Each additional + provides two more hours of protection. The three +s here mean that this sunscreen is sufficient to protect against UVA within six hours.

Precautions

1. It is not that there is no radiation on cloudy days. Sitting under the shade of a tree or wearing a hat can only reduce some of the sun's radiation, but the surrounding water, cement and grass can reflect ultraviolet rays to the skin, causing double damage.

2. The higher the altitude, the stronger the solar radiation. The solar radiation increases by 4% for every 1,000 feet increase.

3. The strongest ultraviolet rays are from 10 am to 2 pm every day.

4. No sunscreen can protect your skin 100%. Even if the SPF is as high as 50, 3% of ultraviolet rays can still penetrate your skin.

5. Opened sunscreen products should be used up as soon as possible. If left for too long, the effective sunscreen ingredients will be reduced and bacteria may grow.

How long does spf30 sunscreen last?

A sunscreen product with SPF 30 can prevent skin erythema for 20*30=600 minutes, or 10 hours!

Sun protection factor: If people stay in the sun for about 15-20 minutes without any sun protection measures, their skin will start to turn red. The sun protection factor of sunscreen is the protection index provided by SPF.

For example, SPF15 means 20 minutes * 15 times = 300 minutes, which means that this sunscreen can protect you from sunburn within 5 hours. SPF30 means 600 minutes, and so on.

Of course, you need to reapply if you are exposed to the sun or after swimming.

A small suggestion: if you are not doing outdoor activities or exposing yourself to the sun, you can use a lower SPF. After all, the higher the SPF number, the greater the burden on the skin. If you are outdoors, it is recommended to use more than 30.

Okay, my friends know that sunscreen SPF30 can protect against the sun for 10 hours.