Lemon: the bright zest that lights up the top notes

Where does lemon come from?

Lemon is the fruit of Citrus limon. Its rind has two layers: an outer coloured zest, aromatic with essential oils, and an inner layer of white spongy pith. As Wikipedia's article on the lemon describes, lemon oil is extracted from the oil-containing cells in the skin: a machine breaks up the cells, a water spray flushes out the oil, and the oil and water mixture is filtered and separated by centrifugation. The Sorrento variety from Italy, with a zest high in lemon oils, is the one traditionally used for limoncello.

What does lemon smell like?

Lemon smells sharp, fresh and juicy, like a freshly grated peel. Much of that signature comes from citral, an aldehyde with a strong lemon scent that is used to fortify lemon oil. The entry on citral describes it as sharp, lemon, sweet, fresh, juicy, tart and green, and names its two forms: neral, a less sweet lemon peel note, and geranial. Citronellal also contributes to the lemon note, but citral is preferred.

What does lemon do in a perfume?

Citrus scents are common top notes, the light materials you smell first, as the article on perfume notes explains and as the class on the fragrance pyramid details. Lemon belongs to the citrus family, and the history of eau de Cologne lists it among the citrus oils of a cologne, next to bergamot, neroli and bitter orange, with lavender, rosemary or petitgrain from orange leaves as possible additions.

What should you know about lemon?

Cold-pressed lemon oil is phototoxic, because it contains furocoumarins. The International Fragrance Association (IFRA) Standard for cold-pressed lemon oil limits it to 2.0% of the finished product in most product categories when the furocoumarin level is unknown, and its use counts toward the combined limit for all phototoxic citrus oils in a formula. Citral is also a known allergen: under EU Regulation 2023/1545, both citral and lemon peel oil must be named on a cosmetic's ingredient list above 0.001% in leave-on products and 0.01% in rinse-off products.