21: Sunscreens


CHAPTER 21
Sunscreens


Angelike Galdi1, Peter Foltis1, Brian Bodnar1, Dominique Moyal2, and Christian Oresajo1


1 L’Oréal Research and Innovation, Clark, NJ, USA


2 La Roche‐Posay Laboratoire Dermatologique, Asnières sur Seine, France


Introduction


Human skin exposure to ultraviolet radiation (UVR) from sunlight can cause many adverse effects. Therefore, it becomes necessary to protect the skin from damaging UVR through various means, one of which is through adequate application of sunscreen, especially when exposed to sunlight for prolonged periods of time.


Effect of sunlight exposure on skin


Ultraviolet (UV) light that reaches the surface of the Earth includes both UVB (290–320 nm) and UVA (320–400 nm). UVB rays are mainly responsible for the most severe damage being acute such as erythema (sunburn), and long‐term skin cancer included, and they can act by directly impacting deoxyribonucleic acid (DNA) and proteins [1]. In the case of sunscreens, the basis for measuring and reporting SPF uses erythema as an endpoint for subjects exposed to UVA and UVB radiation, yet erythema is mostly caused by UVB light (Figure 21.1).


Although SPF can be understood only as a measure of protection from UVB light, it is important that while UVA rays are not directly absorbed by biological targets [3], they can still dramatically impair cell and tissue functions. In particular, UVA penetrates deeper into the skin than UVB. This particularly affects connective tissue, inducing the production of detrimental reactive oxygen species (ROS) which in turn damage DNA, cells, vessels, and tissues [4–9]. In addition, UVA light is a potent inducer of immunosuppression [10, 11] and contributes to the development of malignant melanomas and squamous cell carcinomas [12, 13]. Finally, photosensitivity and photodermatoses are primarily mediated by UVA radiation [14].


It is important to note that under all weather conditions, the UVA irradiance is at least 17 times higher than the UVB irradiance.


For all these reasons, sunscreens must evidently contain both UVA and UVB filters to protect skin from these two associated harmful rays.


Regulatory status of sunscreens


Sunscreen classification


In some zones, sunscreen products can be classified into two main categories according to their purpose:



  1. Primary sunscreens. Products directly intending to protect skin from the effects of the sun, such as beach sunscreens and products used for outdoor activities.
  2. Secondary sunscreens. Products that have a primary use other than photoprotection, such as daily moisturizing creams, antiwrinkle/antiaging creams, etc. In these products, sun protection is necessary to optimize the claimed effect. For this category of products, sun protection is an additional claim.

Sunscreen products can also be classified in terms of regulatory status. In the United States, all products with an SPF claim are regulated as over‐the‐counter drugs (OTC) by the United States Food and Drug Administration (FDA) [15]. Sunscreen products are classified as cosmetics in the European Union (EU), non‐EU European countries (e.g. Russia), most African and Middle‐Eastern countries, India, Latin America, and Japan. They are classified as “special” cosmetic products in China (special cosmetics), Korea and Ethiopia (functional cosmetics), South Africa (under South African Bureau of Standards (SABS) standard), Australia (under standards) [16], and Taiwan (medicated cosmetics). In Canada, they can be either OTC drugs or natural health products (NHP), where in such a case the sunscreen agents should only be “natural” ingredients: titanium dioxide, zinc oxide [17].

Schematic illustration of overlay of erythemal action spectrum and reference solar spectrum irradiance (ASTM G-173) [2].

Figure 21.1 Overlay of erythemal action spectrum and reference solar spectrum irradiance (ASTM G‐173) [2].


Approved UV filters


As of this writing, there are 16 UV filters approved for use in OTC sunscreen formulations in the United States (Table 21.1).


In February 2019, FDA issued the proposed rule, Sunscreen Drug Products for Over‐the‐Counter Human Use in order to finalize the monograph of this product class [18]. The proposed rule included many changes to the existing stayed final monograph issued in 2011. Due to the overwhelming response from industry, professional organizations, physicians, various lobbying group, and concerned citizens, the FDA has delayed the implementation as of this publication date. The proposed changes to the status of currently approved UV filters are summarized below:



  • The FDA requested additional safety data to support the generally regarding as safe and effective (GRASE) status of each UV filter.

    • Currently, only titanium dioxide and zinc oxide are GRASE (Category I).
    • Para‐aminobenzoic acid and trolamine salicylate are proposed to be listed as Category II (not generally recognized as safe and effective). Industry trade groups will not supply data to support inclusion. The remainder of the currently approved filters were proposed as Category III (insufficient data available to permit final classification). Data gaps in safety profiles were identified. It is incumbent on industry (UV filter manufacturers and sunscreen marketers) to supply the requested data.

      • Industry agreed to financially support the safety studies requested for octocrylene, octinoxate, oxybenzone, homosalate, avobenzone, octisalate, meradimate, and ensulizole for inclusion in the monograph as Category I UV filters.
      • All other UV filters listed in previous monographs will not be supported for inclusion in the final monograph and will remain as Category III.

There are two main regulatory routes to market OTC products in the United States: use of a UV filter included in the monograph or an new drug application (NDA). The latter is necessary to obtain the approval of a formula containing a new UV filter, a new concentration for an approved active ingredient, or a new mixture of approved actives. As an example, ecamsule is available in the United States under NDA for four formulas only.


A time and extent application (TEA) is a procedure established by the FDA in 2002 to approve an active ingredient already approved abroad. It allows the FDA to accept commercial data obtained from markets outside of the United States. However, the toxicological data file required for a TEA is similar to that for an NDA. To date, eight UV filters have been submitted to the FDA under a TEA but all require additional safety and toxicological data in order to support inclusion in the monograph as Category I, i.e. GRASE.


Table 21.1 Sunscreens approved in the USA.

























































































Sunscreen approved in the US Maximum concentration (%) λmax (nm) Status
p‐Aminobenzoic acid (PABA) 15 283 Proposed Category II
Avobenzone 3 357 Proposed Category III. Industry to support
Cinoxate 3 308 Proposed Category III. Industry will not support
Dioxybenzone 3 284 and 327 Proposed Category III. Industry will not support
Ensulizole (phenylbenzimidazole sulfonic acid) 4 310 Proposed Category III. Industry to support
Homosalate 15 306 Proposed Category III. Industry to support
Meradimate (menthyl anthranilate) 5 336 Proposed Category III. Industry to support
Octinoxate (octyl methoxycinnamate) 7.5 311 Proposed Category III. Industry to support
Octisalate (octyl salicylate) 5 305 Proposed Category III. Industry to support
Octocrylene 10 303 Proposed Category III. Industry to support
Octyl dimethyl PABA (padimate O) 8 311 Industry will not support
Oxybenzone (Benzophenone‐3) 6 286 and 324 Proposed Category III. Industry to support
Salisobenzone 10 285 Proposed Category III. Industry will not support
Titanium dioxide 25 280–350 Category 1 – GRASE
Trolamine salicylate 12 298 Proposed Category II
Zinc oxide 25 280–390 Category 1 – GRASE
Schematic illustration of common UV filters and spectral coverage.

Figure 21.2 Common UV filters and spectral coverage. DHHB = diethylamino hydroxybenzoyl hexyl benzoate.


In the EU, 27 UV filters are listed in Annex VII of the Cosmetics Directive. In Australia, 26 UV filters are accepted by the Therapeutic Goods Administration (TGA) and in Japan 31 UV filters are allowed.


When comparing the approved UV filters in EU and the United States, only 11 filters appear in common. Because of the importance of being well‐protected against UVA radiation, there are many new UVA filters or broad spectrum UVB/UVA filters, which have been developed and approved in EU, Australia, and Japan. See Figure 21.2 for a list of commonly used UV filters and their spectral coverage


Development of sunscreens


A proper sunscreen product must fulfill the following critical requirements:



  • Provide efficient protection against UVB and UVA radiation;
  • Being stable to heat and to UVR (photo‐stable);
  • Being user‐friendly to encourage frequent application and provide reliable protection; and
  • Cost‐effective.

In order to protect against both UVB and UVA, the sunscreen product must contain a combination of approved UV filters within a complex vehicle matrix. According to their chemical nature and their physical properties, they can act by absorbing, reflecting, or diffusing UV radiation.


Organic UV filters


How do organic filters work?


Organic filters are active ingredients that absorb UVR energy to a various extent within a specific range of wavelengths according to their chemical structure [19], which, absorbing energy, is called a chromophore. The latter consists of electrons engaged into multiple bond sequences between atoms, generally conjugated double bonds. An absorbed UV photon contains energy enough to cause electron transfer to a higher energy orbit in the molecule [19]. The filter that was in a low‐energy state (ground state) is converted into a higher excited energy state. From an excited state, different processes can occur:


Tags:
Nov 13, 2022 | Posted by in Dermatology | Comments Off on 21: Sunscreens

Full access? Get Clinical Tree
Get Clinical Tree app for offline access