Dermatology Made Easy is based on the most popular topics from DermNet NZ's vast array of material. The book combines the essential focus of the ‘Made Easy’ book series with the authority and knowledge base of DermNet NZ's unparalleled resources.
Author: Vanessa Ngan, Staff Writer, 2012.
Para-aminobenzoic acid or PABA as it is more commonly known, is a chemical substance that is found in the folic acid vitamin and also in several foods including grains, eggs, milk, molasses, liver and kidney.
PABA is also prepared industrially for use in sunscreen and local anaesthetic agents. PABA was found to have UVB absorbing properties and in 1943 was patented and became one of the first active ingredients to be used in sunscreen products. Although PABA and its aminobenzoic acid esters (glyceryl PABA, padimate O and roxadimate) are all effective sunscreen agents, they are also strong sensitizing agents and can cause allergic contact dermatitis. Also, in the early 1980s, animal studies with PABA suggested there may be an increased risk of cellular UV damage. For these reasons PABA is now seldom used in sunscreen products.
PABA is the chemical foundation for a group of local anaesthetic agents. These include butethamide, benzocaine, procaine, tetracaine, propoxycaine, and butacaine. Allergic contact dermatitis reactions may occur when these agents are used in PABA sensitive individuals. Benzocaine is the most notorious sensitizer.
PABA sensitivity produces classic allergic contact dermatitis as well as photocontact dermatitis. In PABA allergic individuals, sunscreens containing PABA or its esters can cause a burning or stinging sensation particularly if the product is alcohol-based. However, burning and stinging may also sometimes occur as an irritant reaction in people with sensitive skin, even when not actually allergic to PABA.
Occasionally injection of PABA-derived local anaesthetics to allergic individuals may cause swelling of the oral mucosa (stomatitis) at the site of the injection. Rarely, more severe reactions such as generalised urticaria or anaphylaxis may result.
PABA allergy is diagnosed by performing special allergy tests, i.e. patch tests with 10% PABA in petrolatum.
If you are diagnosed with PABA allergy then avoid exposure to PABA-containing products. Management of PABA dermatitis may be treated as for any acute dermatitis/eczema; this may include treatment with topical corticosteroids and emollients.
Read product labels and avoid products that contain PABA or any of its alternative names. Avoid related substances that you may also be allergic to. This includes sunscreen products containing PABA esters, paraphenylenediamine (PPD) commonly found in permanent hair dyes, sulfonamides, and azo dyes. Ask your pharmacist for advice and a suitable alternative. Alert your doctor and dentist to the fact that you have an allergy to PABA. Your dermatologist may have further specific advice, particularly if you are highly sensitive.
Formula:4-Aminobenzoic acid – C7H7NO2
CAS number: 150-13-0
Appearance: White-grey crystals
Sensitizer: PABA and its esters
Patch test: 10% PABA in petrolatum
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