Oral hygiene products include toothpaste, dental floss, denture cleansers and mouthwashes. Contact reactions to oral hygiene products affect all age groups.

Toothpastes consist of flavourings, preservatives, colouring agents, abrasives, detergents, binding agents, humectants, antiseptics, antacids and fluoride salts. Flavourings are the major cause of allergic contact reactions to toothpaste and there is considerable overlap with foods.

Toothpastes and other oral hygiene products can cause cheilitis (inflamed lips) and stomatitis (inflamed mouth). Specific conditions include:

• allergic contact cheilitis
• irritant contact cheilitis
• contact stomatitis
• perioral eczema due to contact allergic dermatitis or contact irritant dermatitis
• contact leukoderma
• contact urticaria
• discolouration of teeth

Such reactions are however fortunately rare considering how commonly and frequently these products are used.

Allergic contact reactions to oral hygiene products

Who gets allergic contact reactions to oral hygiene products?

Allergy to oral hygiene ingredients is rare, probably due to the rinsing after use. Approximately 30 allergens have been identified in toothpastes and these are present in most.

Females present more commonly than males with contact allergic reactions to toothpastes and other oral hygiene products. This may be due to women becoming sensitized first to other perfumed products.

Overall toothpastes are the second commonest cause of contact cheilitis after lipsticks, but the commonest cause in males.

Clinical presentation

How is contact allergy to oral hygiene products diagnosed?

Patch testing is the first investigation for suspected contact allergy. Baseline standard series are often not helpful in diagnosing contact allergy to dental hygiene products as the common allergens present in these products are not included. Therefore it is important to add an extended toothpaste series and the patient's own products.

There is some discussion in the literature about patch testing with toothpaste ‘as is’ because of irritant reactions to the detergents and abrasives. However some studies report it is possible to distinguish irritant and allergic patch test reactions to toothpastes. The advantage of testing with the patient's own product is that in a significant proportion of cases, the only positive reaction is to the product. However, patch testing to the product may give a false-negative result if the allergen is present in low concentrations.

Some authors recommend confirming the product patch test results using a start-restart test or repeated open application test (ROAT).

Toothpaste companies usually co-operate with dermatologists, providing further information about their product so the allergen can be identified.

Testing can also be useful in identifying alternative products that are likely to be safe to use for the patient.

The cause of an immediate (type I) reaction (contact urticaria) is identified by skin prick/scratch testing. However, the low concentration of the allergen in a product may be too low to give a positive reaction. In one case, prick testing with a mint leaf was positive, but a negative reaction was seen with the patient's mint-flavoured toothpaste.

The ultimate test is ceasing the suspected product and noting the improvement over several weeks.

Treatment

As in all forms of contact allergy, the best treatment is avoidance of the product and allergen if identified. The reaction should resolve within a few weeks.

Allergens reported in oral hygiene products

Toothpaste

Flavourings in toothpastes give the ‘fresh clean taste’ and cover the bitter taste of pyrophosphates in tartar-control toothpastes. And these are the commonest ingredients that cause contact allergy. The most common responsible substances derive from the mint plant:

• Spearmint
• Peppermint
• Menthol
• Carvone

Other allergens reported include:

• Cinnamal – flavouring derived from cinnamon
• Anethole – flavouring derived from star anise, fennel and anise
• Propolis – antiseptic
• Hexylresorcinol – plaque control
• Azulene – anti-inflammatory
• Dipentene – solvent used in cleaning products
• Cocamidopropyl betaine – surfactant
• Parabens – preservative
• Fluoride salts

Dental floss

The common allergens found in dental floss are colophony (E915) and flavourings.

Mouthwashes

Many of the same allergens are found in mouthwashes as toothpaste, added for the ‘fresh clean taste’ flavouring. Cocamidopropyl betaine in a ‘2-in-1 toothpaste-mouthwash’ has been reported to cause allergic cheilitis.

Denture cleaner

This has very rarely been reported to cause contact allergy. However the use of a denture cleaner containing ammonium persulphate on a well-worn acrylic denture was reported to cause allergic contact cheilitis as the persulfate adsorbed to the porous denture with slow subsequent release.

Irritant contact reactions to oral hygiene products

Sodium lauryl sulphate (SLS) is a common detergent and surfactant present in toothpaste. It promotes the formation of lather and may have some anti- microbial effect. As it is a detergent it can cause irritant contact dermatitis, especially of the perioral skin. Several studies suggest SLS may increase the frequency of attacks of aphthous ulcers in those prone to getting them, although one study failed to show any improvement after changing to a toothpaste not containing SLS.

Irritant contact cheilitis may also be caused by the high concentration of pyrophosphates in tartar-control toothpastes.

Discolouration of teeth due to oral hygiene products

Chlorhexidine is a common ingredient of mouthwashes as it kills bacteria. Prolonged use of a chlorhexidine-containing mouthwash can cause discolouration of the teeth and dental restorations. Chlorhexidine can also affect the sensation of taste.