Dear Sir The article on ‘bath-related headache’ (BRH) by Mak et al. (1) makes interesting reading and is an excellent summary of all cases of this type of headache reported so far. We wish to place on record an unusual variant of this type of headache that is seen in Indian patients. Mak et al. have rightly categorized BRH into Type 1 and Type 2. However the differences between these two types have not been specifically highlighted in the article. Analysis of their Table 1 suggests that Type 1 BRH is usually seen in female patients beyond age 45, and presents acutely to the emergency department (ED) with severe explosive thunderclap headache warranting exclusion of subarachnoid haemorrhage: the headaches are shortlasting 4 h), almost always precipitated by hot water, there is no past history of headache, there is no photophobia or phonophobia and, most importantly, the link between the hot bath and headache remits spontaneously. In contrast to this, what they label as Type 2 BRH are the four cases reported by Mungen et al. (2). These patients had a past history of migraine or tension-type headache, they did not present to the ED with severe headache, none of them needed imaging studies to rule out other secondary headaches, they were more easily preventable and remitted after many years. Type 1 BRH has so far been reported exclusively from the Far East, whereas Type 2 has so far been reported only from Turkey. As an extension to this unusual link between bath and primary headaches, we wish to report ‘hairwash’ as an unusual trigger of migraine in Indian patients (3). It is important to mention here that most Indian ladies have long hair that is well-plaited and, since it is time-consuming to dry the long hair after a bath, many do not wet their hair whenever they have their daily bath. It is only on a holiday, when they have more time at their disposal or when there is a special occasion that they have a ‘hair-wash’, and this may be on 2–3 days of the week. It is also not common practice to use perfumes, shampoos or hair

The pathophysiological basis for this remarkable regional variation still defies explanation and has not been convincingly discussed in any of the articles on the subject. One can only conjecture at this stage whether it is due to a genetic or racial variation, whether it is the wet hair that triggers through temperature-sensitive receptors, or whether there is some form of persistent allodynia that manifests intermittently in some migraineurs. Through their article, Mak et al. have begun a search for an explanation as to why this type of primary headache has so far (i) not been reported from the West, (ii) has been reported as acute thunderclap from the Orient, and (iii) has been reported as recurrent migraine elsewhere. It would be stimulating to receive feedback from basic science researchers. Based on the presentation seen in our Indian patients , we would tend to agree with Mak et al. that the non-thunderclap variety of Type 2 BRH would eventually be