Henna is a natural substance that, when applied to the skin as a paste, leaves behind a beautiful brownish-colored stain. It dyes hair, skin, and fabric organically, similar to a black tea dye. Powdered henna leaf as used as a cosmetic in the Middle East has been tested for its antimicrobial qualities against a series of common organisms. It has been shown to be effective against bacteria and some common fungi, but to have only limited potency against Candida albicans and Trichosporon beigelii. Henna is one of the oldest cosmetics known, used as a dye to stain nails, hands, feet and hair. Henna is often used in cosmetic products as a hair conditioner and other preparations have included it for its reputed astringent, anti-dandruff and nail strengthening effects. In its natural state, there is nothing in henna powder that can cause irritation or allergic reactions. Sometimes, the ingredients that are added to the powder to create the paste – such as eucalyptus oil – could possibly serve as an irritant to those with sensitive skin, but that is very rare. Natural henna paste leaves behind a stain on the skin that is a burnt orange or brown color.