Sunscreen: which ingredients to avoid?

It is not uncommon for sunscreens to include fragrances to enhance the sensory experience and mask the unpleasant odour of certain UV filters. Yet, they rank among the leading causes of allergies in skin care products, including sunscreens. These reactions present as redness, with possible swelling, itching and vesicles. Certain fragrance molecules can cause photodermatitis, known as photoallergic contact dermatitis. This occurs when the substance applied to the skin reacts under UV exposure, triggering a skin reaction. It may seem surprising to find such compounds in sunscreens, but they are included for their fragrance function and because not all skin is sensitive to them.

An informative clinical study illustrated this risk: 24 volunteers took part in a phototest using 6-methylcoumarin (6-MC), a fragrance compound used in cosmetic formulations. After six hours’ occlusion on different skin sites with solutions containing 5 %, 1 % or 0.1 % 6-MC, participants were exposed to the minimal erythema dose (MED). The MED is the lowest UV dose required to induce erythema, that is, skin reddening. Results showed that even at 1 % concentration, 6-MC induced a pruritic vesicular reaction, while at 0.1 % participants developed redness and moderate oedema. No effect was observed on untreated control sites, confirming the ability of certain fragrances to sensitize the skin and trigger photocontact allergies.

Our recommendation : If you have sensitive skin, we recommend choosing a sunscreen that is fragrance-free. Any skin type should test the product on the inner elbow at first use before applying it to your face or body.

As mentioned earlier, mineral UV filters, zinc oxide and titanium dioxide, can occur as nanoparticles. These particles offer uniform, transparent UV protection without the whitening effect linked to microscopic filters. However, this is not without drawbacks, as nanoparticles are accused of being able to cross the skin barrier and enter the bloodstream. A 2015 study examined nanometric titanium dioxide. The results showed that on intact skin, nanoparticles remain on the epidermal surface. When the skin barrier is compromised, for example after sunburn or on atopic skin, nanoparticles appear able to penetrate the epidermis and accumulate in the dermis, raising questions about their local and systemic toxicity.

Nanoparticles pose an ecological problem. When rinsed off in the shower or carried into the sea, they disperse into aquatic ecosystems and some studies have shown they have a harmful impact on phytoplankton, a fundamental link in the marine food chain. Their accumulation could unbalance ecosystems and affect biodiversity and ocean health. Studies have shown zinc oxide nanoparticles may contribute to coral bleaching.

To avoid nanoparticles, check the INCI list: the designation “[nano]” must appear. We exclude sunscreen filters in nanoparticle form.

Certain sunscreens sometimes contain essential oils that add a natural scent to the formulation. However, these oils are not always compatible with sun exposure, as they can render the skin more sensitive to UV rays. This applies to citrus essential oils, including bergamot, lemon, sweet orange and grapefruit, which contain furocoumarins. Applying these oils just before sun exposure can cause redness or burns, in other words photodermatitis. This perspective requires nuance. A recent study measured by spectrophotometry the sun protection factor (SPF) of nine essential oils. The measured SPF values ranged from 1.2 to 36.4, with an average around 11.1.

Even though certain essential oils are of interest in sunscreens, it is inadvisable to add them to a finished formulation : this can compromise the product’s stability and photoprotective efficacy.