What are the potential dangers of benzoyl peroxide?

The benzoyl peroxide should be used with caution due to its various side effects. It is known to be a photosensitiser, a bleaching agent and is strongly discouraged in certain specific cases.

• Benzoyl peroxide is a photosensitising substance.

  The benzoyl peroxide is a photosensitiser, more specifically a phototoxic substance. Indeed, it causes immediate skin damage when exposed to UV rays, which generate free radicals whose accumulation leads to damage or destruction of cells. These reactions manifest as redness, similar to sunburn, or hyperpigmentation. They can vary in severity depending on the skin's sensitivity, the concentration, the amount and the frequency of application of the benzoyl peroxide. It is advised to use the product in the evening to avoid sun exposure and the associated side effects.

• The use of benzoyl peroxide results in discolouration.

  Benzoyl peroxide should be used with caution to avoid any contact with the hair. It is recommended to apply it at least half an hour before going to bed, as its strong bleaching power can alter both coloured fabrics and hair.

• Benzoyl peroxide is not recommended in certain instances.

  Benzoyl peroxide presents a moderate risk for the 9 months of pregnancy as well as breastfeeding. This is a precautionary measure as no study has yet highlighted any harmful effect on the development of the foetus or the health of the mother. Finally, precautions should also be taken in children under the age of 12, regardless of their weight.. Patients with wounds, fair skin or using concurrent treatments with other keratolytic and detergent preparations should avoid the application of benzoyl peroxide-based products, as it may delay wound healing, increase photosensitivity in fair skin and intensify skin irritation in patients under concurrent treatment.

Benzoyl peroxide generates benzene through degradation. However, benzene is a carcinogen for humans, classified by the International Agency for Research on Cancer (IARC).

Beyond its potential adverse effects on the skin, benzoyl peroxide is also suspected to be hazardous to human health. A study revealed high concentrations of benzene in 111 samples of over-the-counter benzoyl peroxide-based products, analysed by gas chromatography coupled with mass spectrometry. Among the products tested at room temperature, 34% exhibited benzene levels exceeding the 2 ppm limit, established for pharmaceutical products. To avoid the production of benzene, some dermatologists advise to store in a cool place creams based on benzoyl peroxide, but they are not overly alarmed about the dangers of this ingredient.

To assess the effect of sun exposure on the release of benzene by benzoyl peroxide, a second experiment was conducted by incubating a plate containing 54.5 mg of benzoyl peroxide at 37 °C (body temperature) under a UVA/B lamp for two and a half hours. The results show that sun exposure significantly increases the production of benzene. However, few in-depth studies have been conducted on this phenomenon. Other studies published in the journal have indicated notable differences in heat-induced benzene formation depending on the formulations of benzoyl peroxide-based pharmaceutical products. These results justify further research on other formulations in order to better understand the formation of benzene under the effect of UV rays.