Preservatives, also referred to as biocides or disinfectants, are chemical agents designed to inhibit the growth of bacteria and fungi. Since the 1930s, they have played a crucial role in preventing household goods, textiles, personal care products, and medications from becoming mouldy or decomposing. Today, most cosmetics and industrial products contain preservatives to ensure their longevity and safety.
The primary types of preservatives include parabens, formaldehyde-releasers, and isothiazolinones, such as methylisothiazolinone. While these chemicals are effective in preventing microbial growth, they can cause contact allergic dermatitis in individuals who are sensitive to them.
To safeguard public health, many countries regulate the concentration of preservatives in products and mandate that they are clearly listed on packaging. However, the likelihood of developing a contact allergy increases with higher concentrations of these chemicals.
Contact allergic dermatitis caused by preservatives is more common in women than men and typically manifests in areas exposed to the offending chemical. For instance, a shampoo containing preservatives might cause a rash on the neck, while preservatives in clothing may lead to dermatitis where the fabric touches the skin. Similarly, preservatives in creams can result in irritation in areas where the product is applied.
Symptoms of contact allergic dermatitis include redness, swelling, and blistering in acute cases, or dryness, thickening, and intense itching in chronic conditions. The dermatitis can be intermittent or continuous, making it difficult to distinguish from irritant contact dermatitis caused by external factors like wet work or constitutional dermatitis such as atopic dermatitis.
Occupational exposure to preservatives, particularly in industries like hair stylists where numerous products are used, often presents as hand dermatitis. This type of reaction is known as occupational dermatitis.
Individuals allergic to one type of preservative may tolerate products containing other types of preservatives. However, cross-reactions within the same chemical group can occur, complicating the process of identifying suitable alternatives.
In addition to contact dermatitis caused by preservatives, reactions to cosmetics, topical medications, and cosmeceuticals can result from sensitivity to other components, including fragrances, botanicals, antioxidants, and stabilizers. These reactions may involve sensitive skin, irritant contact dermatitis, or allergic contact dermatitis.
Preservatives are not only found in topical products but are also added to foods to prolong shelf life. While most individuals with contact allergies to preservatives can consume foods containing these substances without issue, there are exceptions. Common food preservatives associated with adverse reactions include sulfites, benzoates, and synthetic antioxidants.
Sulfites, which include compounds such as sulfur dioxide, sodium bisulfite, and potassium metabisulfite, can irritate the lungs and trigger asthma when inhaled as gases. In their liquid or solid forms, they are commonly used in cold drinks, processed meats, dried fruits, and salads and may cause hives.
Benzoates, including benzoic acid and sodium benzoate, are added to various foods and drinks and may cause urticaria, angioedema, and asthma. Synthetic phenolic antioxidants like BHA and BHT used to prevent rancidity in fats and oils, can also result in asthma, rhinitis, and urticaria.
To accurately diagnose a preservative allergy, patch testing is typically the initial step. This process helps identify the specific substances causing the allergic reaction, allowing individuals to make informed choices about the products they use and consume.
Understanding the potential for preservatives to cause contact allergic dermatitis or other adverse reactions underscores the importance of informed product selection and awareness of ingredient labels, particularly for those with known sensitivities.
