So during the periods your body should be kept warm to avoid problems like cramps , headache , dizziness etc.( that's why we use hot water bag to sooth period cramps) . Of course your hair has nothing to do with your period but when you wash your hair , it cools down the body temperature which can lead to above mentioned problems .

Repeating this again , HAIR HAS NOTHING TO DO WITH YOUR PERIODS , ONLY THE COLD ! Even for bathing , one should use lukewarm water during periods . Also , this is the reason why we are told to consume warm or hot food during this time of the month .

I am not forcing anyone to believe this , it's totally up to you to believe it or not . But i don't believe this and It's just that many of them don't know the reason behind it , so we consider it a myth only .

Remember , there's always a reason why our ancestors did things in a particular way and we should also learn from them instead of just calling it myths !