The use of oils (unspecified, but often referring to plant-based oils such as coconut, olive, argan, or castor oil) for supporting the hair and scalp has deep roots in traditional and folk medicine across many cultures. Historically, oils have been applied to the hair to improve shine, manageability, and overall appearance, as well as to moisturize the scalp and reduce dryness or flakiness. In regions such as South Asia, hair oiling is a longstanding tradition believed to promote hair strength and growth, although these claims are primarily anecdotal.

Scientifically, while some plant oils are shown to penetrate the hair shaft (notably coconut oil), reducing protein loss and protecting from damage during washing, robust clinical evidence supporting unspecified "oil" as a class for promoting hair growth or health is limited. Most available research focuses on specific oils rather than an unspecified or generic category. However, traditional use is widely documented, and many people report subjective improvements in hair texture and scalp comfort with regular oiling.

In summary, the use of oil for hair health is primarily justified by tradition, with limited but suggestive scientific support for certain specific oils. The overall evidence level is moderate when considering traditional knowledge and limited clinical data.