Antioxidants

In a formula, antioxidants slow the oxidation that makes oils and fats go rancid, which extends a product's shelf life and helps protect its color and scent. They work by neutralizing free radicals, the reactive molecules that drive oxidation. They are added to oil-based products and the oil phase of creams.

They slow it down, which is exactly why formulators use them. Adding a small amount of an antioxidant like rosemary antioxidant or BHT to a carrier oil, balm, or butter extends how long it stays fresh before it develops that sharp, stale rancid smell. They delay oxidation rather than stopping it forever.

They protect against different things. An antioxidant protects oils from oxidation and rancidity. A preservative protects water-based products from microbes like bacteria, mold, and yeast. A water-containing cream needs both: an antioxidant for the oils and a broad-spectrum preservative for the water. One cannot replace the other.

A very small amount. Most antioxidants work at a fraction of a percent up to around 1 percent. Rosemary antioxidant, for example, is often used between 0.2 and 1 percent. Follow the level on the listing, and do not overdose it, since more will not extend shelf life further.

Rosemary antioxidant, extracted from rosemary, is one of the most effective natural options and is often stronger than vitamin E for the same dose at slowing oil oxidation. Vitamin E (tocopherol) is another common natural antioxidant. Both are used to protect oil-based products from going rancid.

BHT is a synthetic antioxidant used widely and at very low levels in oil-based cosmetics to prevent rancidity and color change. It is used because it is effective at protecting fats. If you prefer a plant-derived option, rosemary antioxidant is a natural alternative that does a similar job.

Add it to the oil phase, ideally early in the process, so it protects the fats from the moment they are combined. Because antioxidants defend oils rather than water, there is no benefit to adding them to a purely water-based part of the formula. Keep the water phase protected with a preservative instead.