Limonene
Limonene is a very common and inexpensive fragrance ingredient found in many plants such as rosemary, eucalyptus, lavender, lemongrass, and peppermint, and is the main component (approximately 50–90%) of citrus peel oil. Its CAS number is 138-86-3 and it is officially classified by CosIng as a deodorant, perfuming agent, and solvent. It is also studied as a penetration enhancer, primarily for lipophilic (oil-loving) compounds. Upon air exposure, limonene oxidizes, and the resulting oxidized form is associated with adverse skin reactions.
Limonene contributes a pleasant scent to cosmetic formulations and has been studied as a penetration enhancer for oil-loving ingredients. Some research has noted its presence in anti-aging formulations, though its primary role remains fragrance.
Oxidized limonene (formed upon air exposure) is a frequent skin sensitizer and can cause allergic contact dermatitis; this risk is particularly relevant for individuals with sensitive skin. It carries EU Cosmetic Restrictions (III/88, III/167, III/168), indicating regulated use limits.
