Bayonet hair is a congenital hair anomaly.
The reason for their development is unknown; it can be assumed that it consists in congenitally weakened hair growth, sometimes due to mechanical blockage of the follicle exit.
In such a hair at the end there is a thickening noticeable to the eye, which gradually becomes thinner towards the free end of the hair. Thus, the upper end of the hair resembles a bayonet, which is why such hair got its name.
Bayonet-shaped hair in humans is not common, and traditionally only individual hairs growing among perfectly normal hair are bayonet-shaped.
Treatment is not required. Bayonet hair grows normally and is a negligible cosmetic defect, since their features are almost not noticeable.