What Does the SPF Number on Sunscreen Lotions Mean?

What Does the SPF Number on Sunscreen Lotions Mean?
SPF stands for "Sun Protection Factor," and on bottles of sunscreen is joined with a number to tell consumers how long the product will protect skin from harmful ultraviolet (UV) rays. However, SPFs and sunblocks are always more complicated than that.

"SPF 30"

Ostensibly, the SPF listed on the bottle times 10 yields the amount of time that a sunscreen offers protection. "SPF 30" for example, should yield 300 minutes when properly applied and used.

International Terminology

"SPF" is almost universally used as a labeling term for sunscreen effectiveness, even in countries where English is not spoken. This makes picking out a sunscreen in places like Bali or Goa much easier.

UVB Rays

The first consideration is that most sunscreens are only effective against one type of UV rays, known as UVB rays. These sunscreens ignore UVA rays, which are harmful, albeit less so than UVB rays.

Sun Variables

American and European agencies test with temperate sun strength, which is obviously much weaker than the concentrated sunlight present near the equator. Exposure time should be considered much reduced there.

Skin Variables

Another variable is the person's skin, as some people are more liable to sunburn than others. A pale person who burns easily is not going to get the same 300 minutes out of an SPF 30 sunblock as a person with normal skin.


Another SPF issue is more sunblock is generally applied in test situations than in regular outdoors conditions. If a thinner coat of sunblock is applied than what was used in the tests, it obviously won't offer the full effect.


Article Written By Edwin Thomas

Edwin Thomas has been writing since 1997. His work has appeared in various online publications, including The Black Table, Proboxing-Fans and others. A travel blogger, editor and writer, Thomas has traveled from Argentina to Vietnam in pursuit of stories. He holds a Master of Arts in international affairs from American University.

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