Sunscreen: which ingredients should be avoided?

Sunscreens can contain fragrances to enhance the sensory experience and mask the unpleasant odor of certain UV filters. Yet they figure among the leading causes of allergic reactions in cosmetic products, including sunscreens. These reactions appear as redness, swelling, itching, or vesicles. Some fragrance molecules can cause photodermatitis, known as photo-contact allergy. This occurs when the applied substance reacts under UV exposure, triggering a skin response. It may seem surprising to find these compounds in sunscreens, but they serve a fragrance function and not all skin types react to them.

A clinical study illustrated this risk: 24 students took part in a phototest using 6-methylcoumarin (6-MC), a fragrance compound integrated into skincare formulations. After six hours of occlusion on different skin areas with solutions containing 5%, 1%, and 0.1% 6-MC, volunteers were exposed to the minimal erythema dose (MED). The MED is the lowest UV dose needed to cause erythema, that is, skin reddening. Results showed that even at 1% concentration, 6-MC could induce an itchy vesicular reaction, while at 0.1% volunteers displayed redness and moderate swelling. No effect was observed in untreated control areas, confirming the ability of some fragrances to sensitize the skin and trigger photocontact allergies.

Our recommendation : If you have sensitive skin, we recommend choosing a sunscreen without fragrance. Regardless of your skin type, test the product on the inner elbow at first use. Then apply it to your face or body.

As mentioned earlier, mineral sunscreen filters—zinc oxide and titanium dioxide—can occur in nanoparticle form. Nanoparticles offer more uniform, transparent UV protection without the whitening effect attributed to microsized mineral filters. This is not without drawbacks, the nanoparticles and are accused of being able to cross the skin barrier and enter the bloodstream. A 2015 study examined titanium dioxide in nanometric form. The results showed that, on healthy skin, nanoparticles remain on the epidermal surface. When the skin barrier is compromised, as after sunburn or in atopic skin, nanoparticles appear to cross the epidermis and accumulate in the dermis, raising questions about their local and systemic toxicity.

Nanoparticles pose an environmental concern. When rinsed off in the shower or carried into the sea, they disperse into aquatic ecosystems, and some studies have shown that they have a detrimental impact on phytoplankton, which is a fundamental link in the marine food chain. Their accumulation could disrupt ecosystems, affecting biodiversity and ocean health. As noted above, studies have shown that zinc oxide nanoparticles can contribute to coral bleaching.

To avoid nanoparticles, check the INCI list: the “[nano]” label is mandatory. We exclude sunscreen filters in nanoparticle form.

Some sunscreens contain essential oils that provide a natural scent. However, these oils are not always compatible with sun exposure, as they can make the skin more sensitive to UV rays. This applies to citrus essential oils such as bergamot, lemon, sweet orange, or grapefruit, which contain furocoumarins. Applying these oils before sun exposure can cause redness or burns—in other words photodermatitis reactions. However, this view deserves nuance. A recent study used spectrophotometry to evaluate the sun protection factor (SPF) of nine essential oils. The SPF values ranged from 1.2 to 36.4, with an average around 11.1.

Although certain essential oils may benefit sunscreens, it is inadvisable to add them to a ready-made formula : this may compromise the product’s stability and photoprotective efficacy.