Sunscreens – Chemical vs. Mineral

ARTICLE:

UV Radiation – Sunlight!

The sun emits energy in all different types of electromagnetic (EM) radiation, such as infrared (IR), visible, and ultraviolet (UV) light. This radiation is in the form of waves characterized by wavelength and energy – see Figure 1.^[1,2] Radiation with longer wavelength has lower energy (eg. radio waves), while radiation with shorter wavelength has higher energy (eg. X-ray waves). Some of this radiation is essential to life on Earth, giving us warmth, vitamin D production, and regular sleep cycles, as well as giving plants energy to photosynthesize.^[3] Higher-energy radiation, however, can cause cellular damage and be harmful to life. Luckily, the gases in Earth’s atmosphere act as a protective barrier to most harmful radiation. These gases include water vapor (H₂O), carbon dioxide (CO₂), and ozone (O₃), and either reflect or absorb certain radiation to prevent it from reaching Earth.^[2] Types of radiation which are able to pass through the atmosphere include radio-waves, IR, visible light, and a small amount of UV. It is this UV light that is harmful to our skin.^[2–4]

Of the radiation that reaches the earth, ultraviolet is the highest in energy and most damaging to our skin, causing sunburn, premature aging, and skin cancer.^[3–5] There are two types of UV radiation of concern:

• UVA:  longer wavelength, lower energy – penetrates the skin’s middle layer (dermis), causing deep cellular damage that contributes to premature aging, and risk of skin cancer.

• UVB:  shorter wavelength, higher energy – reaches only the skin’s outer later (epidermis), causing sunburn and skin cancer, but also the production of vitamin D.

Although the amount of UVA radiation reaching Earth is much greater than that of UVB radiation, it is important to protect our skin from both.^[3] Sunscreens are a convenient and effective way of doing this, however, there are potential ramifications for our overuse of them. So much sunscreen washing off into our rivers and oceans causes a chemical change in the environment that can have significant impacts on the ecosystem (eg. the death of ocean reefs).^[6,7] It is, therefore, important that we understand the chemical composition of the sunscreens we choose and learn best-practices to minimize our negative environmental impact while protecting ourselves from the Sun.

Types of Sunscreens

The protective effect of sunscreens is given as the ‘sun protective factor’ (SPF), which is typically a measure of it’s UVB protection.^[4] The higher the SPF, the more protection to your skin. Sunscreens labeled as ‘broad spectrum’ will offer some degree of both UVA and UVB protection.

There are two main categories of sunscreen filters (ie. active ingredients) based on the way they interact with UV rays:^[4,6]

1. Chemical filters:  absorb UV rays into the skin to deactivate them. These ingredients have the broadest range of UVA and UVB protection.

• aka. ‘organic’ filters*

• eg. avobenzone, octocrylene, dibenzoylmethane, benzophenone, salicylate

• Higher SPF possible

• more likely to cause skin irritation (dermatitis, eczema)

• More likely to bioaccumulate in various aquatic animals (corals, algae, mollusks, vertebrates, etc), and even some terrestrial animals (birds) – this is harmful pollution to the animals and environment.

  
  

2.     Mineral (physical) filters: deflect and scatter UV rays, preventing them from entering your skin. TnO₂ blocks UVB radiation (mainly used in cosmetics), whereas ZnO has a wider range of UVA and UVB radiation.

•  aka. ‘inorganic’ filters*

• eg. zinc oxide (ZnO), titanium oxide (TnO₂)

• Lower SPF, but enough to theoretically provide 97% UV protection (at SPF 30)

• Less likely to cause skin irritation

• May still cause environmental harm but higher concentrations are required (ie. it takes more mineral chemicals to cause harm

  
  

*note:  ‘organic’ in the context of chemistry refers to carbon-based chemicals and does not indicate anything about how “natural” or “sustainably-made” it is. ‘inorganic’ refers to metallic chemicals.

Impact of Sunscreens

Sunscreen is a very practical option for protecting ourselves against UV radiation, but we must be aware that it does have a negative effect on the environment. The study by Chatzigianni et. al. (2022) is an excellent summary of the impact of sunscreens on aquatic life, breaking down the impact of individual sunscreen filters on coral species – see Table 1.^[6] Note that all filters shown have a negative effect, but that of mineral sunscreen is caused by much higher concentrations, meaning that it takes much more of that active ingredient to do harm.

Table 1. Impact of sunscreen filters on coral life, adapted from Chatzigianni et al, Table 1.^[6] The studies from which this data is pulled look at exposure of coral species to different filter concentrations for different periods of time.

This impact on coral reefs is especially important if you are lathering up to go swimming in the ocean, letting your sunscreen wash-off directly into the sensitive environment. But we can image that a similar impact can be felt if we go swimming in freshwater lakes and rivers. If we shower the sunscreen off into our water treatment systems, there is likely to be less of an effect – but we must remember that these chemicals we use will accumulate somewhere, possibly into the landfill and into the earth (where it might impact other species and the food we grow). More rigorous scientific studies are needed to understand the full extent of the impact from UV filters.

We must remember our total impact as a collective – if all humans are using lots of sunscreen, there will be a larger negative impact. Our goal as individuals then, should be to be aware of how much we are using and use alternatives to sunscreen when possible.

Alternative Options to Sunscreen

Sunscreens are a practical option for sun protection, allowing us to enjoy the feeling of the sun’s rays for longer. But, for the sake of the environment, we should use alternatives when possible:

• Stay in the shade – choose trails that have lots of trees or buildings to block the sun

• Clothing – hat and sunglasses are standard but also consider long sleeves – not as comfortable on a hot day, I know, but more guaranteed to both protect you from the sun and have less of a negative impact. Light-weight, UV-protective clothing is available (costs more upfront, but cheaper long-term).

• Certain plant products offer some UV protection, not as much as sunscreens (lower SPF) but a good option for short stints in the sun:  aloe vera^[8,9], seed oils (raspberry, blackberry)^[8,9], olive oil^[10] and coconut oil^[9,10].

Conclusions

For our personal health, it is imperative that we protect ourselves from the sun’s UV radiation that causes sunburn, premature aging, and skin cancer. Sunscreens are a practical option, but their ingredients and chemical biproducts cause harm to the environment, especially in the large amounts that we humans use them. Chemical (organic) filters are active sunscreen ingredients which absorb UV light into the skin and deactivate it – these have higher SPF but are more damaging to the environment. Mineral (inorganic) filters are active ingredients which reflect UV light before entering the skin – these provide up to 97% UV-protection (SPF 30) and are less damaging to the environment.  Both can have a negative impact on the environment (namely studied in aquatic environments and coral reefs), but chemical filters have a greater impact at a lower concentration. It is then important that we are conscious of how much sunscreen we are using, where it goes after we wash it from our skin (eg. ocean, rivers, treatment plants), and to consider alternatives to sunscreen when possible – stay in the shade, UV protective clothing, and natural plant extracts.