Does lemon hydrosol cause photosensitivity?

Lemon hydrosol ((INCI name: Citrus Limon (Lemon) Fruit Water), also known as lemon water, is obtained by steam distillation of the citrus fruit. However, it should not be confused with lemon essential oil, which is more active due to its higher concentration of active ingredients. Lemon hydrosol is actually water infused with a small amount of essential oil. From an organoleptic point of view, it is a colourless liquid, sometimes slightly opalescent, with a characteristic fresh and lemony scent. Lemon hydrosol is a natural ingredient used in the manufacture of various skin and hair care products.

This botanical extract is attributed with numerous properties, among which are anti-inflammatory and antimicrobial virtues. Lemon hydrosol indeed contains several active ingredients that have a detrimental effect on bacteria, including limonene and pinenes. Other active ingredients in its composition help to alleviate pain and facilitate the healing of minor wounds. Finally, lemon water is known to have a unifying action on the complexion and to give a healthy glow effect.

Just like lemon essential oil or lemon juice, lemon hydrosol contains furocoumarins, specifically bergapten and psoralen. These compounds are photosensitising agents known to cause skin hypersensitivity to sunlight. Furocoumarins exert what is known as type I photosensitisation. They absorb the sun's light rays and react through fluorescence, meaning they re-emit the absorbed energy.

Indeed, when furocoumarins are applied to the skin, the energy they emit is directly transmitted to the oxygen atoms present in the epidermis. These become reactive and are then referred to as free radicals. Free radicals are dangerous for the skin and are capable of causing damage to DNA, cells, and certain proteins. This leads to an acceleration of skin ageing and promotes the appearance of wrinkles and fine lines, in the mildest cases, or melasma and cancers, in the most severe cases. The topical application of compounds containing furocoumarins also induces significant burns and is responsible for severe sunburns and irritations.

However, the concentration of furocoumarins present in lemon hydrosol is extremely low. That's why this ingredient is generally not considered photosensitising. Nevertheless, as a precautionary principle, we advise you to limit your sun exposure after applying pure lemon water.

Please note : one should not confuse lemon juice and lemon hydrosol. Lemon juice is highly acidic and photosensitising, due to its high concentration of furocoumarins. That's why it is crucial not to expose oneself to the sun after applying a skincare product containing lemon juice.

• CHABUCK Z. & al. Antimicrobial activity of different aqueous lemon extracts. Journal of Applied Pharmaceutical Science (2013).