Octinoxate The shortened name for Octyl methoxycinnamate – see below for more info.

Octisalate The shortened name for Octyl salicylate, a UVB-absorbing sunscreen ingredient in very widespread use.

Octyl methoxycinnamate A synthetic sunscreen chemical originally derived from balsam of Peru, cocoa leaves and cinnamon leaves, among other ingredients. This is a US FDA (Food and Drink Administration) approved sunscreen and is the most popular chemical sunscreens used worldwide in suncare. (Some questions have been raised about its safety, as with other chemical sunscreens.)

Octyl palmitate Some palmitates can be pore-blocking and may also be linked with contact dermatitis; palmitate ingredients are derived from palm oil, and used to replace mineral oil.

Octyldodecanol An alcohol which spreads nicely and conditions the skin well. Can be irritating.

Octyldodecyl stearoyl stearate An ester from Stearic acid and Octyldodecanol (see above).

Octyldodecyl ricinoleate A combination of Octyldodecanol and an ingredient derived from the castor oil plant, which also has good moisturising qualities.

Oleic acid Obtained from various animal and vegetable fats and oils, this can be slightly irritating to skin in some individuals.

Oleic/Linoleic/Linolenic polyglycerides A synthetic ingredient created from oleic, linoleic and linolenic acids.

Oleth-3 See Oleic Acid and Carboxylic acid (under ‘C’here), from which this is derived.

Oleyl Alcohol In common use in cosmetics manufacture, this is derived from fish oils – and so is not suitable for vegan cosmetics – although it can also be produced synthetically. It’s an emollient, a solvent and a carrier, which (according to some sources) can block pores and/or be irritating to skin.

Oxybenzone A synthetic sunscreen ingredient which works by absorbing UV rays into the skin; it can be an irritant, causing contact dermatitis and – ironically – photosensitivity. One controversial study published in the Lancet by Dr. Cameron Hayden and colleagues at the University of Queensland, Australia, found that Oxybenzone could be absorbed by the skin and was then excreted in urine, and may potentially be linked to hormone disruption, according to Environmental Health Perspectives.