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In vitro assessment of the broad-spectrum ultraviolet protection of sunscreen products.
J Am Acad Dermatol. 2000 Dec; 43(6):1024-35.JA

Abstract

BACKGROUND

There are considerable data to suggest that protection from solar ultraviolet (UV) radiation will reduce the risk of acute and chronic skin damage in humans. Whereas the sun protection factor (SPF) provides an index of protection against erythemally effective solar UV, largely confined to the UVB (290-320 nm) and short-wavelength UVA (320-340 nm) region, there is currently no agreed-upon method to measure broad-spectrum protection against long-wavelength UVA (340-400 nm).

OBJECTIVE

The objective of these studies was to assess the potential of in vitro UV substrate spectrophotometry and subsequent calculation of the "critical wavelength" value as a measure of broad-spectrum UV protection and as a routine, practical procedure for classification of sunscreen products.

METHODS

The spectral absorption of 59 commercially available sunscreen products and multiple experimental formulas with one or more UV filters was measured. Sunscreen product, 1 mg/cm(2), was applied to a hydrated synthetic collagen substrate, preirradiated with a solar simulator, and then subjected to UV substrate spectrophotometry. Multiple determinations from 5 independent samples per product were used to calculate the critical wavelength value, defined as the wavelength at which the integral of the spectral absorbance curve reached 90% of the integral from 290 to 400 nm.

RESULTS

We found that a recognized long-wave UVA active ingredient such as titanium dioxide, zinc oxide, or avobenzone is a necessary but insufficient product requirement for achieving the highest proposed broad-spectrum classification, that is, critical wavelength of 370 nm or more. Although SPF and critical wavelength are largely independent of each other, UVA absorbance must increase commensurate with SPF to maintain the same critical wavelength value. Substrate spectrophotometry and the calculation of critical wavelength can readily account for sunscreen photostability by UV preirradiation. Finally, there is also a strong positive relationship between critical wavelength and a currently available in vivo measure of UVA protection.

CONCLUSION

Determination of critical wavelength by means of UV substrate spectrophotometry provides a rapid, inexpensive, and reliable measure of broad-spectrum protection, which is largely independent of SPF, yet ensures long-wavelength UVA protection commensurate with SPF. The procedure provides a routine, sensitive means of differentiating and classifying sunscreen products and, importantly, obviates the need to subject volunteers to acute exposures of high-dose, nonterrestrial UV, the health risks of which are still poorly understood.

Authors+Show Affiliations

Regional Medical Physics Department, Newcastle General Hospital, Newcastle upon Tyne, United Kingdom. b.l.diffey@ncl.ac.ukNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

11100018

Citation

Diffey, B L., et al. "In Vitro Assessment of the Broad-spectrum Ultraviolet Protection of Sunscreen Products." Journal of the American Academy of Dermatology, vol. 43, no. 6, 2000, pp. 1024-35.
Diffey BL, Tanner PR, Matts PJ, et al. In vitro assessment of the broad-spectrum ultraviolet protection of sunscreen products. J Am Acad Dermatol. 2000;43(6):1024-35.
Diffey, B. L., Tanner, P. R., Matts, P. J., & Nash, J. F. (2000). In vitro assessment of the broad-spectrum ultraviolet protection of sunscreen products. Journal of the American Academy of Dermatology, 43(6), 1024-35.
Diffey BL, et al. In Vitro Assessment of the Broad-spectrum Ultraviolet Protection of Sunscreen Products. J Am Acad Dermatol. 2000;43(6):1024-35. PubMed PMID: 11100018.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - In vitro assessment of the broad-spectrum ultraviolet protection of sunscreen products. AU - Diffey,B L, AU - Tanner,P R, AU - Matts,P J, AU - Nash,J F, PY - 2000/12/2/pubmed PY - 2001/2/28/medline PY - 2000/12/2/entrez SP - 1024 EP - 35 JF - Journal of the American Academy of Dermatology JO - J Am Acad Dermatol VL - 43 IS - 6 N2 - BACKGROUND: There are considerable data to suggest that protection from solar ultraviolet (UV) radiation will reduce the risk of acute and chronic skin damage in humans. Whereas the sun protection factor (SPF) provides an index of protection against erythemally effective solar UV, largely confined to the UVB (290-320 nm) and short-wavelength UVA (320-340 nm) region, there is currently no agreed-upon method to measure broad-spectrum protection against long-wavelength UVA (340-400 nm). OBJECTIVE: The objective of these studies was to assess the potential of in vitro UV substrate spectrophotometry and subsequent calculation of the "critical wavelength" value as a measure of broad-spectrum UV protection and as a routine, practical procedure for classification of sunscreen products. METHODS: The spectral absorption of 59 commercially available sunscreen products and multiple experimental formulas with one or more UV filters was measured. Sunscreen product, 1 mg/cm(2), was applied to a hydrated synthetic collagen substrate, preirradiated with a solar simulator, and then subjected to UV substrate spectrophotometry. Multiple determinations from 5 independent samples per product were used to calculate the critical wavelength value, defined as the wavelength at which the integral of the spectral absorbance curve reached 90% of the integral from 290 to 400 nm. RESULTS: We found that a recognized long-wave UVA active ingredient such as titanium dioxide, zinc oxide, or avobenzone is a necessary but insufficient product requirement for achieving the highest proposed broad-spectrum classification, that is, critical wavelength of 370 nm or more. Although SPF and critical wavelength are largely independent of each other, UVA absorbance must increase commensurate with SPF to maintain the same critical wavelength value. Substrate spectrophotometry and the calculation of critical wavelength can readily account for sunscreen photostability by UV preirradiation. Finally, there is also a strong positive relationship between critical wavelength and a currently available in vivo measure of UVA protection. CONCLUSION: Determination of critical wavelength by means of UV substrate spectrophotometry provides a rapid, inexpensive, and reliable measure of broad-spectrum protection, which is largely independent of SPF, yet ensures long-wavelength UVA protection commensurate with SPF. The procedure provides a routine, sensitive means of differentiating and classifying sunscreen products and, importantly, obviates the need to subject volunteers to acute exposures of high-dose, nonterrestrial UV, the health risks of which are still poorly understood. SN - 0190-9622 UR - https://www.unboundmedicine.com/medline/citation/11100018/In_vitro_assessment_of_the_broad_spectrum_ultraviolet_protection_of_sunscreen_products_ DB - PRIME DP - Unbound Medicine ER -