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About Sunscreens

What Is Sunscreen SPF? 

SPF is the abbreviation for Sun Protection Factor and is the system used worldwide to determine how much protection a sunscreen provides, applied to the skin at a thickness of 2 mg/cm2. This system calculates how much UV radiation (mostly UVB) it takes to cause a barely detectable sunburn on a given person with and without sunscreen applied. For example, if it takes 10 minutes to burn without a sunscreen and 100 minutes to burn with a sunscreen, then the SPF of that sunscreen is 10 (100/10).

 

Currently there is no internationally agreed-upon test for measuring UVA protection in human skin. An estimate is made by a laboratory test in which the proportion of radiation passing through a measured amount of sunscreen is determined. To ensure some protection against UVA, products with physical blocking agents making up some of the active ingredients are recommended.

Two Classes of Sunscreen 

Sunscreens can be broadly classified into 2 groups: chemical absorbers and physical blockers.

 

Chemical absorbers work by absorbing ultraviolet (UV) radiation and can be further differentiated by the type of radiation they absorb, UVA or UVB, or both UVA and UVB.

 

Physical blockers work by reflecting or scattering the UV radiation.

Chemical Absorbers 

The table below is a list of some of the common chemical absorbers available and the protection they provide against the UV range.

 

Chemical
UVB
(290-320nm)
UVA II
(320-340nm)
UVA I
(340-
400nm)
 Aminobenzoic acid derivatives
PABA
Partial None
None
Glyceryl PABA
Partial None None
Padimate O
Partial None None
Roxadimate
Complete
Partial None
Benzotriazoles
Medroxyl Partial
None Partial
 Benzophenones
Dioxybenzone Complete Complete Partial
Avobenzone Complete Complete Partial 
Oxybenzone Complete  Complete Partial
Sulisonbenzone Complete Complete Partial
  Cinnamates
 Octocrylene  Complete  Complete  Partial
Octyl methoxycinnamate  Complete  None  None
Salicylates
 Homosalate  Partial  None  None
Ethylhexyl salicylate  Complete  None  None
Trolamine salicylate  Complete None   None

 

Chemical absorbing sunscreens often contain a combination of ingredients to get coverage against both UVB and UVA radiation. Some are also combined with physical blockers.

 

Some organic formulations may degrade when exposed to sunlight; they may therefore not perform as well as expected.

Physical Blockers 

Physical blockers are effective at protecting against both UVA and UVB radiation. The 2 most common physical blockers are titanium dioxide and zinc oxide.

 

Advantages
Disadvantages
  • Are chemically inert
  • Poor cosmetic appearance
  • Extremely safe
  • Bright fluorescent colors added to improve the cosmetic appearance
  • Protect against the full UV spectrum
 


THINGS TO THINK ABOUT WHEN USING SUNSCREEN

  • How much: The effectiveness of a sunscreen depends on how much of it is applied. Most people apply their sunscreen at about one third of the thickness recommended.

  • How often: The effectiveness of a sunscreen is affected by how often it is applied. Most people forget to reapply it every couple of hours.

  • What type: Alcohol-based lotions, sprays, or gels are better for oily or hairy skin. Creams are suitable for dry skin, and milky lotions are the easiest to apply. Special sticks are suitable for noses, lips, and around the eyes.

  • Broad spectrum: Use a good broad-spectrum sunscreen of at least SPF 30.

  • Take time: It takes 20 to 30 minutes for a chemical absorber sunscreen to be absorbed by the skin, and it can be rubbed off very easily; so apply it at least half an hour before going out in the sun. This does not apply to physical blockers which take effect immediately.

  • Activities: Reapply immediately after swimming, excessive sweating, or if rubbed off by clothing or toweling. This should be the case even if the product claims to be "water resistant."