SPF
Also written as: SPF — Sun Protection Factor
Sun Protection Factor; a numerical measure of how well a sunscreen product protects against UVB-induced erythema, expressed as the ratio of protected to unprotected minimal erythema dose.
Full Definition
Sun Protection Factor (SPF) is a standardized in vivo or in vitro measurement used on sunscreen labeling to indicate the level of UVB protection a product offers relative to unprotected skin. An SPF of 30 means a user can tolerate 30 times more UVB exposure before erythema occurs. SPF does not directly measure UVA protection; this requires separate labeling such as the UVA star system or PPD value. In editorial work, SPF is always written in capital letters with no full stops; values follow immediately (e.g., SPF 50), with no hyphen between the acronym and number in most style guides. Editors should ensure SPF claims in promotional and clinical documents are supported by data from recognized test methods.
Usage
Usage note: No full stops between letters; no hyphen between 'SPF' and the numeric value (SPF 30, SPF 50). Distinguish from UPF (Ultraviolet Protection Factor), which applies to fabric.
In Context
- "The patient information leaflet stated 'Apply SPF 50+ sunscreen daily and reapply every two hours.'" — Patient information leaflet
- "The editor queried whether 'SPF-50' should be written as 'SPF 50' per the house style guide." — Copy-editing query