This paper seems like it’s drawing awfully strong conclusions for such thin data. In particular, there’s one (to me) obvious link which the authors don’t seem to have considered: both mental health care (seeing a therapist, diagnoses of a mental illness, etc) and unusual hair coloration are generally the result of self-introspection.

It seems like the Occam’s Razor explanation of this correlation is not “hair might be a means of scaring or at least confusing potential threats” (????), it’s that people who think more about what they want out of life are both more likely to see a therapist (“hm, I feel terrible a lot, what can I do about that?”) and a stylist (“hm, I need a splash of color, what can I do about that?”).

(The initial part of the discussion section has some interesting hypotheses, including one regarding strong expression of identity as a tool to cope with feeling a lack of control, but the third paragraph seems confused, very speculative, and likely to be contraindicated by the statistical controls.)

[Edit: this comment was reworded and expanded significantly after posting, as I realized I had more thoughts to say.]

> We would submit that the simplest explanation for this relationship can be garnered from the known relationship between borderline personality disorder and extreme, though changeable, expressions of identity. A large study found that the P factor, which we attempted to approximate here, seemed to perfectly correlate with a latent borderline personality disorder factor (Gluschkoff et al., 2021.). Those who score high in neuroticism are plagued by worry and doubt, including about themselves and even about who they are. Bing high in neuroticism strongly correlates with suffering from depression and anxiety (see Nettle, 2007). The world appears to them as a frightening place, beyond their control, meaning that even their sense of "self" can be unclear. In periods of extreme concern, they deal with this by creating - and expressing - clear and strong identity (Fox, 2020). This ameliorates their negative feelings, at least for a period of time, meaning, as this has been found with religion, that their identity may even become less extreme and conspicuous as they enter a period of relatively mental stability (see Hills et al., 2004). Thus, unnatural coloured hair can be regarded as an expression of, and way of negotiating, high levels of neuroticism.

It's statistically unsound bullshit by a far right eugenicist. Can we please move on?

It's nothing new. Body modifications (tattoos, piercings, colored hairs, etc.) have long been correlated with mental illness.