“Red hair, sir, in my opinion, is dangerous”


The quote entitling this post is from a PG Wodehouse book ‘Very Good, Jeeves!’.

We have previously discussed the curious connection between melanoma and Parkinson’s disease. There is also a well known connection between melanoma and red hair. And believe it or not, there is another really strange relationship between Parkinson’s disease and red hair.


Title: Genetic determinants of hair color and Parkinson’s disease risk.
Authors: Gao X, Simon KC, Han J, Schwarzschild MA, Ascherio A.
Journal: Ann Neurol. 2009 Jan;65(1):76-82.
PMID: 19194882

In 2009, researchers from Harvard University found a relationship between hair color and risk of Parkinson’s disease, when they examined the records of 131,821 US men and women who participated in the two large longitudinal studies, the Health Professionals Follow-up Study (HPFS) and the Nurses’ Health Study (NHS).

The HPFS, which started in 1986, sends questionnaires to US health professionals (dentists, optometrists, etc) – aged 40-75.  Every couple of years, members of the study receive questionnaires dealing with diseases and health-related issues (e.g. smoking, physical activity, etc). The questionnaire is supplemented by another questionnaires which is sent every four years, that deals with dietary information.

The NHS study – which was established in 1976 and then expanded in 1989 – has also collected questionnaire-based information from 238,000 registered nurses. Similar to the HPFS, every two years the study participants receive a questionnaire dealing with diseases and health-related topics.

In their study, the investigators found 264 of the male and 275 of the female responders to the HPFS and NHS questionnaires had been diagnosed with Parkinson’s disease. Of these individuals, 33 were black haired, 418 had brown hair, 62 were blond and 26 were redheads. Given that redheads make up just 1% of the general population but 5% of the people who were diagnosed with Parkinson’s disease in their study, the authors suggested that red haired people have a higher risk of developing Parkinson’s disease. Interestingly, they found a stronger association between hair color and Parkinson’s disease in younger-onset of PD (that is being diagnosed before 70 years of age) than those with age of onset greater than 70 years. When they took health and age related matters into account, the authors concluded that people with red hair are almost four times more likely to develop Parkinson’s disease than people with black hair.

NOTE: This result does not mean that people with red hair are definitely going to develop Parkinson’s disease, it simply suggests that they may be more vulnerable to the condition. And we should add that this result have never been replicated and we are not sure if anyone has ever attempted to reproduce it with a different database.

So how does (or could) this work?

The short answer is: we really don’t know.

The long answer involves explaining where there are no connections:

Red hair results from a genetic mutation. 80% of people with red hair have a mutation in a gene called MC1R – full name: melanocortin-1 receptor. Another gene associated with red hair is called HCL2 – ‘Hair colour 2’. We know that the connection between red hair and Parkinson’s disease is not genetic, as there is no association between MC1R mutations and Parkinson’s disease (for more on this, click here). We are not sure about HCL2, but this gene has never been associated with any disease.

What we do know is that redheads:

  • are more sensitive to cold (for more on this, click here)
  • are less responsive to subcutaneously (under the skin) administered anaesthetics (for more on this, click here)
  • suffer more from toothaches (for more on on this, click here)
  • are more sensitive to painkillers (for more on this, click here)
  • require more anesthetic for surgery (for more on this, click here)

Common myths associated with red hair include:

  • redheads bled more than others (this is not true – click here)…but they do bruise easier!
  • redheads are at greater risk of developing endometriosis (this is not true – click here)
  • redheads are more frequently left-handed (I can find no evidence for this, so I’ll put it in the myth basket until corrected).

There is also a strange link between red hair and multiple sclerosis, but it is too complicated to understand at the moment (women with red hair are more vulnerable to multiple sclerosis than men with red hair, for more on this, click here).

How any of these findings relates to Parkinson’s disease is unclear – we provide them here for those who are interested in following up this curious relationship.

One important caveat regarding this study is that incidence rates of Parkinson’s disease in countries with very high levels of red hair do not support the relationship (PD & red hair). In Scotland, approx. 10% of the population have red hair (source), and yet the England has a higher incidence of Parkinson’s disease (28.0/10,000 in England vs 23.9/10,000 in Scotland – source).

It may well be, however, that there is no direct connection between red hair and Parkinson’s disease. And until the results of the 2009 study mentioned above are replicated or supported by further findings, we here at the ‘Science of Parkinson’s disease’ shall consider this simply as a curious correlation.