Isononyl isononanoate Occurs in cocoa and oil of lavender, from which an ester is produced by a reaction between alcohol and nonanoic acid (which occurs in geranium).

Inositol Derived from corn, this belongs to the vitamin B family.

Iodopropynol butylcarbonate A widely-used preservative which can be irritating and allergenic; it should not be used in more than an 0.1 per cent concentration, and is not allowed in aerosol products.

Iron oxides (CI 77491, CI 77492, CI 77499)  See CI 77491, CI 77492 and CI 77499 for more info under ‘C‘ – here.

Isoamyl p-Methoxycinnamate A sunscreen ingredient originally derived from cinnamon; cinnamate ingredients can be allergenic to some skins.

Isobutylparaben – one of the ‘contentious’ paraben family of preservatives, widely used for its anti-fungal action. Few ingredients trigger such violent debate as parabens. We have always taken a precautionary approach, although it appears that several of the studies that link parabens with breast cancer, for instance, were flawed (or at least flimsy). Some parabens, however, can be irritating. The bottom line is that we would welcome much more research into this thorny subject. There are many alternatives to parabens appearing in formulations as manufacturers find creative ways to avoid using them – partly a response to the fact that so many brands want to declare themselves ‘paraben-free’.

Isodecyl neopentanoate A synthetic ingredient used as a preservative even in some natural products.

Isoeugenol A fragrance ingredient that smells strongly of vanilla which is derived from Eugenol. It can be skin-sensitising, and must by law be listed as a separate fragrance component on labels because of this.

Isononyl isononanoate A synthetic extract (which can come from lavender and cocoa, originally), it’s used in moisturisers, make-up, sunscreens and hand creams – and also used to create fruit flavourings in both foods and lip products.

Isopropyl jojobate Derived from jojoba oil; valuable for lip glosses, eye creams, anti-agers, blushers and products with an SPF.

Isopropyl palmitate Deployed as a moisturising and thickening ingredient, this ingredient is derived from palm – and is in widespread use.

Isopropylparaben See Isobutylparaben, above, for our thoughts on this family of ingredients.

Isopropyl titanium triisostearate Synthetic compound derived from fatty acids, used in beauty products as an emollient, emulsifier and moisturising element.

Isostearyl acid A complex mixture of fatty acids, similar to Stearic acid – see under ‘S‘ – here.

Isostearyl neopentanoate A synthetic ingredient used as an emollient; it can be pore-blocking.