Tea tree oil (Melaleuca alternifolia) has been traditionally used by indigenous Australians for a variety of skin conditions, including rashes and minor wounds. In modern times, its application has expanded globally, driven by its known antimicrobial and anti-inflammatory properties. Several laboratory studies have demonstrated that tea tree oil exhibits broad-spectrum antimicrobial activity against bacteria and fungi, which can help prevent secondary infections in skin rashes. Additionally, in vitro and animal studies suggest that components of tea tree oil, such as terpinen-4-ol, can inhibit the production of inflammatory mediators, potentially reducing redness and swelling associated with rashes and hives.

Human clinical evidence, however, is limited and of variable quality. Some small studies and case reports suggest that topical tea tree oil preparations may help relieve symptoms of inflammatory skin conditions, including dermatitis, but there are no large, high-quality trials specifically on rashes or hives. Allergic reactions, including contact dermatitis, can occur in some individuals, so caution is warranted. While the scientific rationale for its use is plausible and there is some supporting evidence, the overall strength of the clinical data is modest, justifying a rating of 2 out of 5.