Sunscreens by Design: Cosmeceutical Additions for Photoaging

One of the most important topical products to consider in the realm of mitigating the degree of extrinsic photoaging is that of regular sunscreen use. As part of the evolving changes seen in sunscreen formulation, many have come to be designed with specific dermatological goals in mind. Much research has been directed toward the photoprotective effects of various natural agents, particularly herbal and nutrient-derived antioxidants.

Sunscreen use offers an established benefit on numerous skin conditions associated with both acute and chronic sun exposure. Examples of such conditions include skin cancers such as basal cell carcinoma, squamous cell carcinoma, and melanoma; signs of skin aging; photodermatoses, such as polymorphic light eruption, solar urticaria, and drug/herbal-induced photosensitivity; as well as the worsening of skin concerns such as rosacea and hyperpigmentation concerns like melasma.¹, ², ³ In the years since its general adoption during the 1970s, sunscreen product formulations have evolved. One of the most important adjustments has been the inclusion of sunscreen filters providing coverage for the ultraviolet A (UVA) in addition to UVB spectrum. Since that time, the sunscreen market has blossomed into a wide array of focused and specialty products, often formulated with additional cosmeceutical ingredients. This allows for sunscreens to offer an increased range of applicability in the management of a variety of skin concerns. This article will focus on the impact of UV radiation on the mechanisms underlying skin aging and provide insights into the specific cosmeceutical ingredients in sunscreens designed toward photoaging and hyperpigmentation.

Sunscreens: A Basic Background

The American Academy of Dermatology’s current recommendations for sunscreen application are as follows:⁴

• Minimum sun protection factor (SPF) of 30.
• Used daily and all year around.
• One ounce of sunscreen is the amount recommended to adequately cover all exposed areas.
• To ensure optimal absorption, sunscreen should be applied at least 15 minutes prior to sun exposure.
• Sunscreen should be reapplied every two hours, or immediately after swimming/excess sweating.

With the labelled SPF only being achieved if sunscreen is applied at an application density of 2 mg/cm², one of the primary concerns relating to sunscreen usage is the underapplication of it onto the skin.⁵ This explains the AAD’s recommendation of one ounce which, for ease of recall, approximates to the amount of sunscreen which fills a one-ounce shot glass. Another researched and effective strategy toward protecting against underapplication of sunscreen is to simply use a “double application” approach. By applying sunscreen twice over across exposed areas of skin, various studies have found the application density is increased to levels much closer to the ideal of 2 mg/cm².⁶, ⁷ Two categories of sunscreen filters are currently approved for use in North America: chemical (aka organic/soluble) and mineral (aka inorganic/insoluble). Key aspects of each filter ingredient are highlighted in Table 1.

Table 1: Key Aspects of Sunscreen Filters Ingredients^{8, 9, 10}

Cosmeceutical Additions to Sunscreens Directed Toward Photoaging

It is easy to appreciate the heavy marketing efforts and excitement often generated around various topical agents and formulas directed toward slowing the signs of skin aging. However, the most important topical agent in this regard is that of regular sunscreen use. Its role can often be overlooked, especially with other age-defying and often expensive cosmeceuticals getting the limelight. However, this simple, albeit less flashy, topical is an essential component toward countering the primary driving force behind extrinsic skin aging, that of UV light. Multiple studies have explored the importance of sunscreen use in mitigating various measures of the skin aging process;¹¹, ¹², ¹³ however, after understanding all the mechanisms behind UV damage, there is in fact a growing interest to research ingredients to enhance the effects of sunscreens.

To put this in context, we will briefly review the photoaging process. Common signs of photoaging include the development of fine and deep wrinkles; skin laxity; dryness; texture changes toward, for example, rougher or leathery skin; and pigmentary changes (including uneven or mottled skin tone and solar lentigines/age spots). It has been estimated that up to 80% of the signs of facial aging are attributable to the effects of UV light.¹⁴ Both UVB and UVA are implicated in this process, with UVA having a strong potential to penetrate the dermal layer of skin.¹⁵ Here, chronic UV exposure acts to generate reactive oxygen species (ROS) which activate transcription factor AP‑1. This activation is key, given how it works to simultaneously suppress procollagen formation, activate matrix metalloproteinases (MMPs) to degrade collagen, and activate nuclear factor‑kappa B (NF‑κB), which can induce further inflammation and itself amplify ROS generation. UV radiation is also central to the development of elastin degradation (with concurrent accumulation of abnormal elastin fibres), to the depletion of the cutaneous antioxidant network, and in triggering the processes leading to hyperpigmentation (such as the worsening of melasma, pigmentation over previous acne lesions, uneven/mottled skin tone, and age spots).¹⁶, ¹⁷

With this as a basis, we can better appreciate how researchers and sunscreen formulators have been keen on exploring the effects of adding cosmeceutical actives, in particular antioxidants, to further impede the progression of photoaging. This reflects the need to find other ingredients to mitigate against ROS generation and photoaging. Despite the crucial role of broad-spectrum sunscreens in countering the effects of UV light, some researchers have speculated that their ability to limit ROS production may be complemented by the addition of antioxidants, given the estimate that traditional sunscreens on their own reduce ROS formation by only about 55%.¹⁸ Antioxidant inclusion in sunscreens is also being explored for other benefits as well. These include the stabilization of sunscreen filter ingredients in the formula,¹⁹ as well as the use of antioxidants, like beta-carotene and resveratrol, to reduce the ability of chemical sunscreen filters from penetrating past the stratum corneum layer of the epidermis and moving deeper into the skin’s dermal layer.²⁰

A high volume of preclinical research has been directed toward exploring the UV-protective effects of various antioxidants. These have been summarized in various review articles.²¹, ²², ²³, ²⁴, ²⁵ The bulk of this evidence has been established through in vitro and animal studies, although more human trials are emerging. Some of the common antioxidant cosmeceutical additions incorporated in sunscreens include the agents described in Table 2.

Table 2: Common Antioxidant Cosmeceutical Agents Incorporated in Sunscreens

Human trials exploring the effects of antioxidant-enrichened sunscreen on measures of photoaging are emerging. Although most of the trials to date are relatively small, they demonstrate a noted benefit of adding antioxidant compounds over the use of sunscreen alone in preventing measures of UV‑induced photoaging and hyperpigmentation,⁶⁶, ⁶⁷ as well as against the signs of photoaging and hyperpigmentation caused by visible light ⁶⁸, ⁶⁹ and infrared radiation which accounts for the sensations of heat/warmth felt from sunlight.⁷⁰ Below is a summary of two emerging human clinical research.

A five-day preliminary study analyzed the clinical effects of an antioxidant-enrichened sunscreen.⁷¹ Five subjects with an age range of 18 to 40 years and of Fitzpatrick types I and III (a scale used to estimate an individual’s potential for skin photodamage), served as their own controls by applying to separate areas of buttock skin both an SPF25 moisturizing sunscreen containing an antioxidant mixture, as well as the same SPF 25 moisturizing sunscreen without the antioxidant mixture. A third area of skin, with no applied product, was exposed to simulated UV light, and finally a fourth area with both no product and no simulated UV exposure was designated as control. A solitary dose of simulated solar radiation was applied to the test and control areas at a level of twice the predetermined minimal erythema dose. Histologic evaluation via punch biopsy was undertaken on the fourth day. Primary endpoints included quantification of epidermal Langerhans cells (the depletion of which serving as a surrogate for UV‑induced immunosuppression) and levels of collagen-degrading MMP‑1 (the increased expression of which is characteristic in photodamaged skin). The antioxidant mixture included vitamin C (in the form of aminopropyl ascorbyl phosphate), vitamin E, caffeine, Echinacea pallida extract, Chamomilla vulgaris essential oil, as well as some unique cosmeceuticals like gorgonian extract, which is a type of coral also known as sea whip, which is used as a soothing agent to protect from irritation. Both the SPF25 alone and the SPF25-and-antioxidant mixture topicals were found to prevent Langerhans cell depletion, with no significant difference between the two. However, significant findings were noted in relation to measures of MMP‑1. The SPF25 formula alone led to a 43% reduction of MMP‑1 compared to unprotected UV‑exposed skin control (p < 0.002). The SPF25-and-antioxidant mixture led to a 60% reduction in MMP‑1 production compared to the same control (p < 0.0001). Finally, the 17% greater decrease in MMP‑1 levels found for the SPF25-and-antioxidant mixture versus the SPF25 without antioxidants was also found to reach significance (p < 0.05).

Another study measured free-radical production from the skin of 40 subjects exposed to a 50 J/cm² dose of visible light.⁷² Such exposure led to a significant 85% increase of free radicals compared to baseline levels (p < 0.05). An evaluation demonstrated a positive effect for an antioxidant-enrichened sunscreen containing feverfew (Tanacetum parthenium) extract, soy extract, and gamma-tocopherol in relation to the visible light–induced free-radical production. Both the group exposed to visible light with no sunscreen ^n = 24 and that exposed with non–antioxidant-enrichened sunscreen ^n = 12 experienced an increase in free-radical production. A significant decrease in free-radical production, by 54%, was found only in the group using antioxidant-enrichened sunscreen ^n = 12 as compared to those using sunscreen without antioxidants (p < 0.05).

Challenges of Formulation

Challenges are faced by sunscreen formulators in integrating antioxidant-enrichened sunscreen formulas. First is achieving the desired and simultaneous effects of sunscreens, which are needed on top of the stratum corneum, and antioxidants, which need to penetrate past the outer layer and concentrate within the dermal and epidermal tissues.⁷³ Second, the mere presence of an antioxidant does not guarantee an effect. A formulator needs to select those agents with not only a high antioxidant capacity, but also to be present in a sufficient-enough concentration to have an effect.⁷⁴ Keep in mind that we do not always know what that ideal concentration is for all antioxidants, or if the concentration needs adjustment when included into a sunscreen formula. Future research will hopefully help elucidate these details.

Other Common Additions to a Photoaging-Focused Sunscreen Formula

Photoaging-focused sunscreens will often incorporate other cosmeceutical actives with established use in photoaging. These can include the likes of retinol, niacinamide, and various peptides. Additionally, various moisturizing ingredients, such as hyaluronic acid or glycerin, can complement the formula by providing a fast-acting mode of skin plumping and smoothening. To build upon the hyperpigmentation-preventing effects of sunscreen itself, some formulas will further include cosmeceutical actives with a known skin-lightening effect. Once again, the likes of niacinamide and vitamin C may provide for such benefit. Beyond these, licorice root extract, unfermented soybean extract, and certain peptides like tetrapeptide‑30 (tetrapeptide PKEK) may be utilized for this purpose as well.⁷⁵, ⁷⁶

The use of sunscreens as part of one’s overall sun-protection behaviour has fortunately become more commonplace in our society. This has led to the emergence of sunscreen products with cosmeceutical additions tailored toward mitigating the signs of both photoaging and hyperpigmentation. The bulk of cosmeceuticals used in this regard has focused on various antioxidants. Although more human studies are needed to reveal their potential effects, preliminary trials offer an example of how such agents could be of benefit. Further studies will also help clarify some of the formulation challenges encountered by manufacturers when seeking to combine antioxidants and other cosmeceuticals into sunscreen products. As these details emerge, we may be on the cusp of witnessing a transformation whereby sunscreens transition into a more complete form of sun-protective products.