Tea tree oil (Melaleuca alternifolia) has been traditionally used for a variety of skin and nail ailments, but there is also scientific evidence to support its use for certain nail conditions, particularly fungal infections (onychomycosis). Several clinical studies and in vitro investigations have shown that tea tree oil has antifungal properties effective against dermatophytes, the main group of fungi responsible for nail infections. For example, a double-blind randomized study published in the "Journal of Family Practice" (1994) found that topical application of 100% tea tree oil was as effective as clotrimazole solution in improving symptoms of toenail onychomycosis, though complete cure rates were low for both.

The mechanism is thought to involve terpinen-4-ol and other components of tea tree oil, which disrupt fungal cell membranes. However, while there is evidence supporting its antifungal properties, the effectiveness of tea tree oil in fully curing nail fungus is limited, and results are often less robust compared to conventional antifungals. Most studies report moderate improvement in nail appearance and reduction in symptoms rather than complete eradication of infection.

In summary, scientific evidence supports the use of tea tree oil to support nail health primarily in the context of mild fungal infections, but it should not be relied upon as a sole treatment for severe or persistent cases. More rigorous, large-scale clinical trials are needed to fully establish its efficacy and safety profile.