Derived from a small Australian tree, tea tree oil is a natural oil that has been used as a homeopathic remedy for coughs and skin healing for centuries. Its main benefit when it comes to skin is as a powerful antimicrobial agent — it kills the bacterial invaders that cause acne and inflammation. This function is effective against all types of acne, from smaller blemishes and whiteheads to blackheads and larger cystic acne, and it is safe for use during pregnancy.