What are preservatives?
Preservatives may also be called biocides and disinfectants. They are chemicals that inhibit the growth of bacteria and fungi. They have been used since the 1930s to keep household goods, textiles, personal care products and medications from going mouldy or decomposing. Most cosmetics and industrial products contain preservatives.
The most important classes of preservatives are parabens, formaldehyde-releasers, and isothiazolinones, including methylisothiazolinone. They all may cause dermatitis in some susceptible persons.
In many countries, regulations limit the concentration of preservatives and require preservatives to be listed on the package. In New Zealand, every medicine that contains an antiseptic or preservative must be labelled with a statement of the nature and amount of the antiseptic or preservative (Medicines Regulations 1984). Cosmetics must comply with the Consolidated Cosmetic Products Group Standard (ERMA).
The higher the concentration of preservative, the more likely that some people will develop a contact allergy to it.
How does contact allergy to preservatives present?
Preservatives occasionally cause contact allergic dermatitis. Preservative allergy is more common in women than in men. It results in dermatitis in areas exposed to the responsible chemical. For example, a preservative in a hair shampoo may cause a rash on the neck; a preservative in a textile may result in dermatitis where the clothing touches the skin, and one in a cream results in dermatitis wherever it has been applied.
The affected skin may become red, swollen and blistered (acute dermatitis) or dry, thickened and intensely itchy (chronic dermatitis). Dermatitis may occur intermittently or continuously. It may be difficult to distinguish contact allergic dermatitis to preservatives from irritant contact dermatitis (eg, wet work) or constitutional dermatitis (eg, atopic dermatitis).
Preservative allergy often presents as hand dermatitis, including occupational dermatitis — for example in hairdressers, who use many different products containing preservatives.
People who are allergic to one type of preservative may be able to safely use products containing alternative agents. However, cross-reactions can occur, particularly within the same chemical group.
Further information about preservatives
Contact allergy to preservatives is discussed in individual topic pages.
- Benzalkonium chloride
- Imidazolidinyl urea
- Isopropynyl butylcarbamate
- Isothiazolinone mix
Other reactions to personal care products
Reactions to cosmetics, cosmeceuticals and topical medicaments may also be due to sensitive skin, irritant contact dermatitis, and allergic contact dermatitis to other components such as fragrances, botanicals, antioxidants, stabilisers and so on.
Preservatives in foods
Natural and artificial preservatives are added to many foods to extend shelf life and stop them going bad (food additives). Although most people with contact allergy to preservatives can safely eat foods containing preservatives, there are exceptions. Food allergy is actually more often caused by the food itself.
The most common preservatives in food causing adverse reactions are sulfites, benzoates and antioxidants. They can do so via irritant and allergic mechanisms.
Sulfites include sulphur dioxide, sodium sulphite, sodium bisulphite, sodium metabisulphite, potassium bisulphite and potassium metabisulphite. As gases, they may irritate the lung and trigger asthma. More often they are used in liquid form in cold drinks including fruit juices and wine or sprayed onto foods. They are used as solids to preserve smoked and processed meats, dried fruit and salads. They can cause urticaria.
Benzoic acid, sodium benzoate and parabens are added to food and drinks but also occur naturally in prunes, cinnamon, tea and berries. They may cause urticaria, angioedema and asthma.
Synthetic phenolic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are used to prevent fat and oils turning rancid when exposed to air. They can cause asthma, rhinitis and urticaria.