Protection Factor Assay (SPF)
Final Monograph CFR 64 No. 98, May 21, 1999
determine the Sun Protection Factor (SPF) of sunscreens products for
more than 25 healthy, fair-skinned male or female human subjects of
skin types I, II and III (sensitive and normal) are used. A "screening"
test of 5 subjects may be performed to determine whether or not the
test article is delivering the anticipated level of sun protection.
test within 2 weeks of receipt of samples
Finish test within 2-3 weeks
Report issued within 2 weeks of study completion
4 oz. (125 mL or g)
FDA Monograph recommended standard sunscreen control, 8% homosalate
(HMS), with a mean SPF value of 4.47 + 1.279, is provided by the testing
150 watt Xenon Arc Solar Simulator, equipped with electronically-controlled
shutter release and dosage control system (Solar Light Co., Phila,
PA), having a continuous emission spectrum in the range of 290 to
assessment of dermal response by a trained evaluator
FDA, Sunscreen Drug Products For Over-the-Counter Human Use: Final
Monograph, as described in the Federal Register, Vol. 63, No. 98,
May 21, 1999 pp 27666-27693.
Prior to SPF testing, each subject's sensitivity to UV-B on their
unprotected skin is determined, ie, the Minimal Erythema Dose (MED).
Application and Test Sites
Test areas (10 cm x 5 cm) are delineated on the subject's back between
the beltline and the scapulae and 100 mL of the test article are evenly
applied at a density of 2 mL or mg per square centimeter. After allowing
the test article to dry for 15 minutes, sub-test areas are irradiated
with one of a geometric series of UV-B exposure doses. These exposure
doses are based upon each subject's MED and the expected SPF of the
Immediately after exposure, any skin responses are recorded.
Twenty-two to 24 hours after irradiation, all exposure sites are examined
by an evaluator who is unaware of which formulation or UV radiation
was administered to which site.
Evaluations are conducted under a warm white fluorescent light bulb
providing illumination of 450-550 lux.
Determination of SPF
To obtain an SPF value, the erythema effective exposure (Joules/cm2)
(MED) for protected skin is divided by the erythema effective exposure
for unprotected skin:
MED (Protected Skin)
SPF values and the standard deviation(s) are determined. The upper
5% point from the t distribution table with N-1 degrees of freedom
is calculated (t). The ts is computed (A). The label SPF equals the
largest whole number less than x - A.
monograph-labeling designations are:
Product Category Designation
Rejection of Data
an MED response is not elicited either on the treated or unprotected
skin sites, or a response is randomly absent, or the subject is non-compliant,
test data will be rejected.