what is Para-aminobenzoic Acid (PABA)?

Daniel Judd BSc MBiol
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What is Para-aminobenzoic Acid (PABA) 

Para-aminobenzoic Acid (PABA) is a small organic molecule with a controversial history of use in sunscreen. It’s found naturally in microbes like bacteria and yeast which use it build vitamin B9, also known as folate. Unlike bacteria, we humans can’t do this folate building and must instead get fully assembled folate through our diet. Despite PABA not being an essential part of your diet, it can probably be found in your intestines as the friendly bacteria that live their make it themselves.

In the 1940s, PABA was introduced as an active ingredient in sunscreen. It remained popular until the 1980s where some tests implied it may be damaging to the skin and could in fact increase damage from UV rather than block it.

 

How does it work? 

UV light from the sun can be seriously damaging to your skin, causing sunburn, collagen damage, DNA damage and cancer. The UV light that reaches us can be split into UVA and UVB. UVA makes up most of the UV that reaches us and can cause DNA damage by making reactive molecules called free radicals. UVB makes up a smaller fraction of the total UV and can cause direct damage to the DNA, leading to mutations and possibly cancer.

PABA can absorb some of the UVB light that hits the skin, preventing it from entering the body and damaging the DNA. Unfortunately, it does not absorb any UVA rays which can pass through PABA sunscreens leading to free radical damage in the form of aged looking skin and possibly skin cancer.

Modern sunscreens sometimes use chemicals based on PABA that better absorb UVA and some UVB. Other molecules that fully absorb UVB can also be mixed in. Mineral sunscreens like titanium dioxide fully absorb both UVA and UVB.

 

Side effects

Side effects:

PABA can cause severe allergic reactions, causing both contact and photo-contact dermatitis. Irritation can also occur without an allergy to PABA.

While some studies on cells and animals suggested PABA may increase UV damage, an extensive European Commission committee found that there was no evidence of PABA triggering mutations under UV light.

Contraindications:

PABA can interrupt the action of sulphonamide antibiotics.

 

Other names 

para-Aminobenzoic acid, p-Aminobenzoic acid, 4-Aminobenzoic acid, Vitamin B10, Vitamin Bx, Bacterial vitamin H1

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