Olive oil is synonymous with the Mediterranean diet, heralded for its healthiness after scientists studied the meals of Greeks, Italians and Spanish households. Beyond using it in food, it makes for a great natural hair oil.
Olive oil works wonderfully as a hair conditioner in at least two ways. It's great at locking in moisture. One reason is because it has an "emollient function by sealing the cuticle and trapping the moisture inside" the hair shaft as summarised by Venkataram Mysore and Arpita Arghya on 'Hair Oils: Indigenous Knowledge Revisited'. By sealing the cuticle, the hair shines and glistens after applying the olive oil.
For hair types that are thicker or more curly, relying on natural sebum to migrate from the hair follicle down the hair after shampooing will result in frizzy, static hair. So using olive oil provides the extra help it needs. Because of its deeply penetrative capabilities, olive oil is able to moisturize inside the hair shaft itself.
In the 'Investigation of penetration abilities of various oils into human hair fibers', the researchers concluded that oils high in monounsaturated fats penetrated easily into the hair and olive oil has one of the highest concentrations. Therefore, it can double up as a hair mask or a deep conditioner when used with wet hair when the hair cuticles are more open.
Olive oil may increase the strength of the hair because of a fatty molecule called lineoic acid. While there’s usually only 3-21% of this acid in olive oil, the paper by Si Hyun Lee and Cheunsoon Ahn highlighted the improvement of hair strength in bleached hair which is noticeably weaker due to processing.