---
kind: "section"
citation: "21 C.F.R. § 352.70"
title: "21"
number: "352.70"
heading: "Standard sunscreen."
url: "https://uscodex.org/cfr/21/352.70"
---

# §352.70. Standard sunscreen.

- (a) **Laboratory validation.** A standard sunscreen shall be used concomitantly in the testing procedures for determining the SPF value of a sunscreen drug product to ensure the uniform evaluation of sunscreen drug products. The standard sunscreen shall be an 8-percent homosalate preparation with a mean SPF value of 4.47 (standard deviation = 1.279). In order for the SPF determination of a test product to be considered valid, the SPF of the standard sunscreen must fall within the standard deviation range of the expected SPF (i.e., 4.47 ±1.279) and the 95-percent confidence interval for the mean SPF must contain the value 4.
- (b) **Preparation of the standard homosalate sunscreen.**
  - (1) The standard homosalate sunscreen is prepared from two different preparations (preparation A and preparation B) with the following compositions:
  - (2) Preparation A and preparation B are heated separately to 77 to 82 °C, with constant stirring, until the contents of each part are solubilized. Add preparation A slowly to preparation B while stirring. Continue stirring until the emulsion formed is cooled to room temperature (15 to 30 °C). Add sufficient purified water to obtain 100 grams of standard sunscreen preparation.
- (c) **Assay of the standard homosalate sunscreen.** Assay the standard homosalate sunscreen preparation by the following method to ensure proper concentration:
  - (1) **Preparation of the assay solvent.** The solvent consists of 1 percent glacial acetic acid (V/V) in denatured ethanol. The denatured ethanol should not contain a UV radiation absorbing denaturant.
  - (2) **Preparation of a 1-percent solution of the standard homosalate sunscreen preparation.** Accurately weigh 1 gram of the standard homosalate sunscreen preparation into a 100-milliliter volumetric flask. Add 50 milliliters of the assay solvent. Heat on a steam bath and mix well. Cool the solution to room temperature (15 to 30 °C). Then dilute the solution to volume with the assay solvent and mix well to make a 1-percent solution.
  - (3) **Preparation of the test solution (1:50 dilution of the 1-percent solution).** Filter a portion of the 1-percent solution through number 1 filter paper. Discard the first 10 to 15 milliliters of the filtrate. Collect the next 20 milliliters of the filtrate (second collection). Add 1 milliliter of the second collection of the filtrate to a 50-milliliter volumetric flask. Dilute this solution to volume with assay solvent and mix well. This is the test solution (1:50 dilution of the 1-percent solution).
  - (4) **Spectrophotometric determination.** The absorbance of the test solution is measured in a suitable double beam spectrophotometer with the assay solvent and reference beam at a wavelength near 306 nanometers.
  - (5) **Calculation of the concentration of homosalate.** The concentration of homosalate is determined by the following formula which takes into consideration the absorbance of the sample of the test solution, the dilution of the 1-percent solution (1:50), the weight of the sample of the standard homosalate sunscreen preparation (1 gram), and the standard absorbance value (172) of homosalate as determined by averaging the absorbance of a large number of batches of raw homosalate:

## Notes

### Authority

Authority: 21 U.S.C. 321, 351, 352, 353, 355, 360, 371.

### Source

Source: 64 FR 27687, May 21, 1999, unless otherwise noted.