Structure and Properties of some of the organic compounds in sunscreens
Avobenzone
Avobenzone is a dibenzoylmethane derivative and it exists in the ground state as a mixture of the enol and keto forms, favouring the chelated enol. This enol form is stabilized by intramolecular hydrogen-bonding within the β-diketone. Its ability to absorb ultraviolet light over a wider range of wavelengths than many other sunscreen agents has led to its use in many commercial preparations marketed as “broad spectrum” sunscreens. Avobenzone has an absorption maximum of 357 nm. Although Avobenzone is considered safe, disintegration products may have significant health impacts and persist in the environment.
Ecamsule
Ecamsule is an organic compound which is added to many sunscreens to filter out UVA rays. It is a benzylidene camphor derivative, many of which are known for their excellent photostability.
para-aminobenzoic acid
para-aminobenzoic acid or PABA is an intermediate in the synthesis of folate by bacteria, plants, and fungi. It is a UVB absorber, meaning it can absorb wavelengths between 290 and 320 nm. Patented in 1943, PABA was one of the first active ingredients to be used in sunscreen. The first in vivo studies on mice showed that PABA reduced UV damage. In addition, it was shown to protect against skin tumours in rodents. Animal and in vitro studies in the early 1980s suggested PABA might increase the risk of cellular UV damage. On the basis of these studies, as well as problems with allergies and clothing discoloration, PABA fell out of favour as a sunscreen. However, water-insoluble PABA derivatives such as padimate O are currently used in some products.
Padimate O
Padimate O is an organic compound related to the water-soluble compound para-aminobenzoic acid or PABA. Padimate O absorbs ultraviolet rays, thereby preventing direct DNA damage by UV-B. However, the thus-excited padimate O molecule may then react with DNA to produce indirect DNA damage, similar to the effects of ionizing radiation.
