Aluminum-based compounds are typically the common deodorant ingredients, along with fragrances, salts, and parabens. Potassium alum performs a similar function as aluminum, but is often used in deodorants that are labeled natural. The aluminum-based compounds used in antiperspirant deodorants form plugs in the sweat ducts in the armpits which prevent sweat from escaping to the surface of the skin. Skin harbors odor-causing bacteria that proliferate when they mix with sweat, increasing body odor.
Deodorants that are labeled "natural" often use mineral salts, or potassium alum, to inhibit perspiration. It does so differently than the aluminum-based compounds. Instead of plugging up the sweat ducts, or pores, it forms a barrier over the skin preventing sweat from escaping. Potassium alum is a naturally occurring mineral, however, it can be made synthetically in a laboratory.
Natural deodorants designed for sensitive skin often use witch hazel as the active ingredient. Witch hazel is derived from a low-growing shrub also commonly called witch-hazel. It has skin soothing and anti-inflammatory properties and is used in many different herbal remedies. Witch hazel is commonly found in mens' aftershaves to heal and prevent razor burn. In deodorant, it acts as an astringent, which causes pores to constrict, thereby reducing the amount of sweat released.
Fragrances are very common deodorant ingredients. They can be synthetically made, or they can come from plants. Plant derived fragrances are often called essential oils. For those with sensitive skin, there are also fragrance-free deodorants and antiperspirants.
Parabens were once common deodorant ingredients, but are being used less frequently due to health concerns. They're easy to find in a list of ingredients as the word “paraben” is part of the name, for example, methylparaben, butylparaben, propylparaben and so forth. Triclosan and propylene glycol are other common deodorant ingredients. Triclosan, which is classified as a pesticide by the US Food and Drug Administration (FDA), kills bacteria and is fat-soluble, meaning it's stored in body fat.
Propylene glycol is a form of mineral oil that is used to speed up the absorption rate of some of the ingredients in deodorants and antiperspirants. It can cause an allergic reaction in some people. It is a humectant, which means it helps skin or hair retain moisture.