Sunscreen: which ingredients to avoid?

UV filters are the pillars of sunscreens: without them, products could not protect skin from the sun and its hazards (photoageing, sunburn, hyperpigmentation, skin cancers...). There are two main categories of sunscreen filters: mineral (or physical) filters, such as titanium dioxide and zinc oxide, and organic (or chemical) filters. The latter are subject to controversy, owing to their potential impact on human health and the environment.

Among the most contested UV filters is oxybenzone (INCI: Benzophenone-3), the octocrylene, the homosalate or even the octinoxate (INCI: Ethylhexyl Methoxycinnamate). These molecules are accused of crossing the skin barrier and reaching the bloodstream. Some studies have suggested possible endocrine-disrupting effects, that is an interference with the hormonal system, although the data remain subject to debate. Rat studies have shown that octocrylene can affect thyroid hormone metabolism. Rodent studies indicate that octinoxate may alter the reproductive system and reduce sperm count. However, it is difficult to draw firm conclusions for humans, these findings are not directly transferable and the tested concentrations exceed those present in sunscreens.

In addition to these health concerns, the environmental impact of chemical filters is debated. Several studies suggest that certain UV filters, such as octocrylene, octinoxate, oxybenzone, and enzacamene (INCI: 4-Methylbenzylidene Camphor), can disrupt marine wildlife and contribute to the phenomenon of coral bleaching. This is why some regions, such as Hawaii, have banned their use. Note that this risk applies to zinc oxide nanoparticles, which can alter the symbiosis between corals and zooxanthellae, the single-celled algae essential to their survival.

Criticism of these UV filters does not mean they are prohibited, as current scientific data are insufficient to conclude on their risk. However, by precautionary principle, we exclude sunscreen filters that raise health or environmental concerns.

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.

Never apply pure jasmine essential oil to your skin expecting SPF 30+: essential oils must always be diluted with care as they can irritate the skin. These findings indicate that a formulator may consider incorporating a photoprotective essential oil into a sunscreen.

The researchers went further: after measuring the SPF of the essential oils alone, they evaluated the effect of adding them to a sunscreen. They tested a control formula without essential oil, then the same cream enriched with 0.3%, 0.6%, and 0.9% jasmine essential oil, and likewise with lilac essential oil. The results, presented below, show that adding less than 1% essential oil significantly increases SPF, in a dose-dependent manner.

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.

• KLIGMAN A. M. & al. Photocontact allergy to 6-methylcoumarin. Contact Dermatitis (1978).

• CROSERA M. & al. Nanoparticles skin absorption: New aspects for a safety profile evaluation. Regulatory Toxicology and Pharmacology (2015).

• ZHONGHUA C. et al. TiO2 nanoparticles in the marine environment : Physical effects responsible for the toxicity on algae Phaeodactylum tricornutum. Science of the Total Environment (2016).

• SUH S. & al. The banned sunscreen ingredients and their impact on human health: a systematic review. International Journal of Dermatology (2020).

• HUTCHISON J. E. & al. Zinc oxide‑induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation. Photochemical & Photobiological Sciences (2021).

• KEARNS G. & al. Sunscreens: potential hazards to environmental and human health. Frontiers in Marine Science (2024).

• ZITO P. M. & al. Sunscreens and photoprotection. StatPearls (2025).

• HUMAIRA N. & al. Evaluation of sun protection factor (SPF) value of essential oils and its application in sunscreen cream. IOP Conference Series: Earth and Environmental Science (2025).