Homosalate in Sunscreens: Hidden Risks for Breast Cancer Recovery

Sunscreen safety is often judged by SPF numbers and water resistance — but few people consider what the ingredients themselves may be doing inside the body. Homosalate, a chemical UV filter still found in many mainstream sunscreens and cosmetics, is now under global scrutiny for its potential to interfere with breast cancer treatment and recovery.

A Common Ingredient With Uncommon Risks

Homosalate is a salicylate-based UV filter designed to absorb UVB rays. It’s been used for decades, yet new research suggests it may do far more than just protect skin. Studies have found that homosalate can mimic oestrogen — a natural hormone that fuels many breast cancers — and promote the growth and spread of tumour cells in laboratory settings. At the same time, it may interfere with the effectiveness of certain treatments, giving cancer cells an advantage in surviving and spreading.

In recognition of these concerns, the European Union has restricted homosalate to just 0.5% in leave-on cosmetics, after safety assessments found higher levels unsafe for long-term use. However, in other markets, it remains widely used in products applied daily to the face and body — often in combination with other oestrogenic filters.

How It Affects the Body

Endocrine-disrupting chemicals (EDCs) like homosalate can imitate hormones, altering natural signalling in sensitive tissues such as the breast. In vitro studies show that even low concentrations can stimulate the growth and movement of human breast cancer cells. Recent findings also indicate that homosalate may encourage cancer cells to release microscopic “messenger” particles known as extracellular vesicles (EVs), which can help tumours communicate, spread, and become more resistant to therapy.

Safer Sunscreen Science

For consumers recovering from or at risk of breast cancer, ingredient choice matters. Mineral-based sunscreens formulated with non-nano zinc oxide offer broad-spectrum protection without hormonal or systemic effects. Zinc oxide acts as a physical barrier, reflecting and scattering UV rays rather than absorbing them, and is recognised by the FDA as generally safe and effective (GRASE) and approved by the TGA for use in sunscreens up to 25%.These photostable, skin-friendly filters avoid the endocrine and genetic concerns now linked to several organic UV absorbers — including homosalate, oxybenzone, and octocrylene — while still meeting global cosmetic and therapeutic standards.

Technical Summary (Evidence-Based Overview)

Independent studies have confirmed that homosalate shows hormone-like activity in laboratory tests and can influence the behaviour of breast cancer cells. In a landmark in vitro analysis, Jiménez-Díaz et al. (2013) found that homosalate interacted with both oestrogen and androgen receptors, leading to changes in cell growth and hormonal balance. This supports earlier evidence that some UV filters used in cosmetics may act as endocrine disruptors. More recently, Zhang et al. (2024) reviewed the effects of cosmetic UV filters on human cell models and reported that homosalate exposure increased cell growth, migration, and invasion — changes that could make breast cancer cells more aggressive and less responsive to treatment.

Together, these findings indicate that long-term or repeated exposure to homosalate could contribute to hormone-related cell changes. In contrast, non-nano zinc oxide remains biologically inert and non-hormonal, providing safe, broad-spectrum UV protection recognised by global regulators.

The Takeaway

Ongoing research continues to reveal the biological complexity of common UV filters — and homosalate stands out as one of the most concerning. For formulators and brands committed to health-conscious innovation, replacing hormone-active filters with GMP-certified, non-nano zinc oxide is not just a safer option — it’s a regulatory and ethical imperative.

Zhang, Y., Tu, L., Chen, J., Zhou, L. (2024). Interference mechanisms of endocrine system and other systems of endocrine-disrupting chemicals in cosmetics – In vitro studies. International Journal of Endocrinology, 2024. 1-20. https://doi.org/10.1155/ije/2564389

Jiménez-Díaz, I., Molina-Molina, J. M., Zafra-Gómez, A., Ballesteros, O., Navalóna, A., Real, M., Sáenz, J. M., Fernández, M. F., Olea, N. (2013). Simultaneous determination of the UV-filters benzyl salicylate e, phenyl salicylate, octyl salicylate, homosalate, 3-(4-methylbenzylidene) camphor and 3-benzylidene camphor in human placental tissue by LC–MS/MS. Assessment of their in vitro endocrine activity. Journal of Cromatography B, 936, 80-87. http://dx.doi.org/10.1016/j.jchromb.2013.08.006