Sun protection factor

Quotient of the erythema threshold dose of protected skin ( MED) and the erythema threshold dose of unprotected skin.

SPF (sun protection factor) = MED with sun protection factor/MED without sun protection factor

Thus, the sun protection factor indicates how many times longer one can expose oneself to the sun with sunscreen X without risking dermatitis solaris than would be possible with the respective individual self-protection time. For example, a sun protection factor (SPF) 6 means a six times longer exposure time before the onset of erythema within 24 hours.

In Germany, the sun protection factor is indicated on products with the abbreviation LSF or SF + number.

The French term IP stands for "Indice de Protection" and is identical with the German term.

The American factor SPF stands for Sun Protecting Factor and is calculated differently than LSF/SF and IP.

For this reason, about 30% must be subtracted from an SPF to obtain a German or French value. Thus, an SPF 24 can be roughly compared with an LSF/SF or IP 16.

The UV measurements are generally performed with a monochromatic UV radiation source, whereby the biologically relevant UV spectrum between 320 and 400 nm is determined before and after application of a defined amount of a light stabilizer using various spectroscopic methods (e.g. spectrofluorimeter, e.g. Fluorolog 3 by Yvon Horiba, Edison, NJ, USA)
(Rucolo Jnior et al. 2014; de Oliveira DN et al.2015).

1. Behar-Cohen F et al (2013) Ultraviolet damage to the eye revisited: eye-sunprotection factor (E-SPF®), a new ultraviolet protection label for eyewear. Clin Ophthalmol 8:87-104.

2. de Oliveira DN et al.(2015) In vitro evaluation ofSun
   Protection Factor and stability of commercial sunscreens using massspectrometry
   . J Chromatogr B Analyt Technol Biomed Life Sci 988:13-19.

3. Hönigsmann H (1992) Sun protection. Dermatologist 43:395-401

4. Reinau D et al (2015) The meaning and implicationof
   sun protection factor. Br J Dermatol 173:1345.

5. Ruvolo Junior E et al. (2014) New noninvasive approach assessing in vivosun
   protection factor (SPF) using diffuse reflectance spectroscopy (DRS) and
   invitro transmission. Photodermatol Photoimmunol Photomed 30:202-211.