Shining the Light on Sunscreen

Thaddaus R. Hellwig, PharmD, BCPS; Elizabeth M. Gripentrog, PharmD Candidate; Kathryn S. Templeton, PharmD Candidate


US Pharmacist 

In This Article

Sunburn Protection Factor (SPF)

SPF is the numeric measurement of how effective a sunscreen is at preventing sunburn.[2] SPF is calculated by dividing the amount of UV rays required to produce minimal erythema on skin to which a sunscreen product has been applied by the amount of UV rays required to produce minimal erythema on unprotected skin.

Historically, SPF values have ranged from 2 to greater than 100. This has led to an assumption that products with higher SPFs have significantly better sun protection (i.e., SPF 30 being twice as protective as SPF 15). This assumption may be inaccurate because an SPF 15 product blocks about 93% of UVB rays from penetrating the skin, while an SPF 30 product blocks about 97% of UVB rays. Historically, SPF measurements were quantified solely by UVB protection, with possibly no UVA coverage included in the product.[5]


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