Capsaicin is the main active ingredient in chili. When used externally (in a reasonable dose), chili stimulates blood circulation and is perfect for, among others, anti-cellulite cosmetics. Patch tests have shown that there is no “significant irritation or contact dermatitis,” so it does not irritate the skin when used correctly.
Capsaicin is also able to stimulate the immune system, and chili oil has a moderate level of vitamin C, which can help increase the production of white blood cells while also acting as an antioxidant to ease the load on the immune system.