Lip Sun Protection Factor of a Lipstick Sunscreen

Abstract

Background and Objective: There is a well-documented need for effective human UVA and UVB photoprotection. Since there are important anatomical variations, the sun protection factor (SPF) of a lipstick sunscreen was measured on the anatomical site intended for use. Methods: The SPF tests were performed according to Federal US and European COLIPA guidelines. Prior to performing a test on the lip, the minimal erythemal dose (MED) of the unprotected back skin was determined. Subsequently, the sunscreen SPF was measured on the anatomical target site (lip). The evaluator was blinded with respect to scoring the SPF of each sunscreen treatment. Individual test sites were assigned to one of the following treatment conditions: (1) no treatment (MED of unprotected skin); (2) test formulation; (3) reference standard. Results: The MED on unprotected back skin was found to be 25% lower than on unprotected lip skin. The SPF of the lipstick sunscreen was measured 2 units lower than the SPF determined in the classical way on the back skin. Conclusion: It was hypothesized that the higher MED of the lower lip compared with back skin was due to the adaptation of this tissue to the continuous exposure to UV radiation.

The porcine snout – an in vitro model for human lips?

“…This difference, combined with the lack of follicles, might be the reason for the different biological response of the lips to topically applied products or to solar radiation, compared to the reaction of the skin on the forearm or the back. The minimal erythema dose on the human lip was shown to be higher than that on the skin of the back, whereas the sun protection factor (SPF) on the lip was higher than that on the back (7). This increased SPF could be caused by a more homogeneous distribution of the sunscreen on the lip surface, compared to the distribution on the back.…”

“…In addition, in vivo and in vitro studies on human lips are limited due to the lips' small surface area. Under these conditions, comparative tests of different formulations cannot be performed (7). Therefore, it is pivotal to find an in vitro model for human lips.…”

Ultraviolet protective performance of photoprotective lipsticks: change of spectral transmittance because of ultraviolet exposure

“…The transmittance of great amounts of UVA radiation may at first sight appear to be inconsequential if one considers the reference action spectrum for UV‐induced erythema and the estimated action spectrum for induction of squamous cell carcinomas by UV in the skin of hairless mice (55), since the erythemogenic and carcinogenic effect of a transmitted UVB dose is much more pronounced than the biological effect of a transmitted UVA dose. Furthermore, a recent publication indicated that the vermilion of human lips appears to be less UV‐sensitive than the skin in other areas of the body (56). Nevertheless, both UVB and UVA were defined as carcinogenic factors by the IARC (57) and sub‐erythemogenic UVA doses are responsible for various biological effects, e.g., induction of photosensitivity diseases (58) and skin photodamage (59).…”

Assessment of thickness of photoprotective lipsticks and frequency of reapplication: results from a laboratory test and a field experiment

“…Working or playing in an environment with reflecting surfaces (snow field, glacier) represents a special risk situation for structures of the face (upper lip) usually shaded by the facial profile. Histologically, the lips are covered by a thin epidermis with a very thin horny layer and are less pigmented than other regions, although it was reported recently that lip skin appears to be less sensitive to UV radiation than ‘normal’ skin 25 . Outdoor workers have an increased risk for the development of lip cancer or premalignant lesions.…”