PABA (P-Aminobenzoic Acid) & Derivatives
This compound was used extensively in the 1950's and 1960's. It has since fallen out of favor for several reasons:
- It doesn't effectively absorb the wavelengths of UV light compared to newer active ingredients.
- It is not water soluble, and so must be used in an alcohol-based solution.
- Some people become sensitive to the compound after contact, and can have an allergic reaction to subsequent exposures.
- It can discolor both cotton and synthetic fabrics, and the yellow stain can become permanent after sun exposure.
PABA is no longer a common ingredient in sunscreens.
Many of the PABA derivatives are water-soluble and do not penetrate the skin, thus avoiding photo contact dermatitis. The most common derivative, padimate O is now used in very few sunscreens. All PABA derivatives provide only partial UVB and no UVA protection.
These are not very effective sunscreen agents. However, they are often used because they are stable, non-sensitizing (not usually causing a bad reaction), and water-insoluble. Being water insoluble means that they can be used in a water-resistant or waterproof sunscreen. They provide full UVB coverage, but no UVA protection.
These compounds are UVB blockers but have poor substantivity (waterproofness). They are generally found in combination with other agents. An example is octylmethyl cinnamate, which is abbreviated OMC.