PABA (Carcinogenic sunscreen or bacteria food?)
10th July 2006
PABA, or para-aminobenzoic acid, was used as a sunscreen some time ago. Most sunscreens are simply organic molecules that aren’t too soluble in water (so they don’t wash away) that absorb UV light (and convert it into heat). There are other kinds, like zinc oxide creams, that just provide an opaque/reflective layer. PABA, however, is of the first type.
It is also a biosynthetic precursor to folic acid in many bacteria. This is a profoundly essential nutrient, especially for rapidly dividing cells. This applies to pregnant women (hence the inclusion of extra folate in prenatal vitamins) and most bacteria, which tend to be pretty busy dividing. Since people don’t depend on the PABA-Folate conversion system (because we don’t have it), PABA has been used as a drug target for antibiotics. These are the ancient sulfa drugs, which predate even penicillin. Here is the structure of PABA:
Today, PABA is not in sunscreens because of allergy and carcinogenicity concerns (close analogues are safe and included, though). Sulfa drugs have also fallen by the wayside, largely because of allergy and poor efficacy compared to the modern stuff.
Interestingly, furosemide (Lasix) contains a sulfa-drug like structure, but works on a completely different pathway (it’s a diuretic).
See you tomorrow!