Tea Tree Oil (Melaleuca alternifolia) has a long history of traditional use for various skin conditions, but it is also supported by some scientific evidence for its anti-inflammatory and antimicrobial properties, which are relevant to the management of rashes and hives. Several in vitro and animal studies indicate that tea tree oil can reduce inflammation by suppressing pro-inflammatory mediators such as histamine and cytokines (Carson et al., 2006). Small clinical studies and case reports suggest that topical application of diluted tea tree oil may alleviate symptoms of allergic skin reactions, including rashes, by reducing redness, swelling, and itching.

However, direct clinical trials specifically investigating tea tree oil for the treatment of urticaria (hives) or general rashes in humans are limited, and most evidence is extrapolated from its known effects on similar inflammatory skin conditions like eczema or contact dermatitis. Additionally, tea tree oil can itself cause allergic reactions or dermatitis in some individuals, particularly if used undiluted or in high concentrations.

Overall, while there is a plausible scientific basis for using tea tree oil topically to help with rashes and hives due to its anti-inflammatory properties, the evidence is modest and not robustly established through large-scale clinical trials. Therefore, it is generally rated as having limited (low to moderate) scientific support for this specific use.