What are hydroperoxides of limonene and linalool?
Limonene and linalool are fragrance chemicals extracted from the peel of citrus fruits (limonene) and herbs, flowers, and woods (linalool).
Limonene and linalool are themselves occasional contact sensitisers. However, on exposure to oxygen in the air, both substances oxidise into hydroperoxides which are much more potent sensitisers. As such, limonene and linalool are an increasingly recognised source of allergic contact dermatitis.
Where are hydroperoxides of limonene and linalool found?
- Personal care products eg, shampoos, conditioners, moisturisers, deodorants, and cosmetic products
- Household products eg, washing up liquids and detergents
- Industrial products and processes
Those sensitised may tolerate newly opened products, but after a period of time after the pack has been opened, the parent fragrance oxidises which can cause an allergic dermatitis. Due to this delayed oxidisation, a freshly opened product that is used daily at home may not cause problems, but an identical older opened product eg, those kept with holiday toiletries, may elicit a reaction.
Who gets contact allergy to hydroperoxides of limonene and linalool?
Ten percent of individuals investigated for a suspected contact dermatitis were found to be allergic to these hydroperoxides. Allergy was more common in women and those aged over 40 years.
What are the features of contact allergy to hydroperoxides of limonene and linalool?
Sensitised individuals will develop contact dermatitis on exposure to the hydroperoxides wherever there has been skin contact, such as where the personal care product has been applied to the skin.
- Commonly affected sites include:
- The axillae
- Face
- Trunk
- Hands.
- The rash is often:
- Red
- Swollen
- Vesicles and even blisters may develop.
How is contact allergy to hydroperoxides of limonene and linalool diagnosed?
Patch testing confirms the diagnosis — hydroperoxides are included in some of the standard patch test series. Those sensitised will develop a positive patch result; tests are read 48 and 96 hours after application of the allergen to determine patch test reactions.
Patch testing details:
- Hydroperoxides of limonene 0.3% in petrolatum
- Hydroperoxides of linalool 1% in petrolatum.
How is contact allergy to hydroperoxides of limonene and linalool treated?
Offending products containing the hydroperoxides must be discontinued. The eczema is treated by the application of a topical steroid until the allergic reaction settles [see Allergic contact dermatitis].
What should I do to avoid hydroperoxides of limonene and linalool?
- Avoid products which contain the offending parent allergen (limonene or linalool)
- Individual constituents are listed on the product label or insert.
- Product manufacturers’ websites usually have a tab which reveals the list of individual constituents which is often easier to read than minimised print on the package label.
- Use perfume- or fragrance-free products as a safe alternative
- “Parfum” is best avoided.