Brief Answer:
Self care/ control precipitating factors/ expert advise

Detailed Answer:
Hi XXXX,
Thanks for asking through Health care magic. I have read & understood your concern.
You have unbearable scalp itching after you feel hot... you have heat sensitivity. Any thing that damages or dries scalp skin can add up to heat sensitivity .
It can be-
- medication like blood pressure medicines, allergy medicines,
decongestants
- allergy to ultra-violate rays
- Hyperthyroidism
- Anxiety.
- negligence to hair care
Exposure to heat damages skin epithelium/ hair roots to cause itching increased sweating , anxiety add up in the symptom & the vicious circle of scalp sensitivity & damage of scalp& itching goes on till exposure to heat is controlled.So to break the vicious circle becomes important while such sensitivity can be removed with help of expert allergy specialist

* Management-
- To exclude adding factors like hyperthyroidism,allergy, use of medicines
that increase the symptoms, anxiety with help of expert
consultation/investigations/counselling & self effort.
-Try to avoid exposure to heat. Stay in a cool atmosphere as far as
possible/avoid going out in strong heat/ use protective covers
( umbrella, hat )when it becomes must to move in sun.
-drink lot of water,juices through out the day & while being in sun
heat(can take cool water .
- Eat healthy nutritious & fresh food avoiding allergens if found.
- Hair care..with protection from getting hot / exposure to sunlight.
Routine hair care with-
. Daily combing with wide toothed comb
. light oil massage at roots with tea tree oil/ aloe vera oil/ coconut
oil twice a week followed by head bath with XXXXXXX warm water,
using light shampoo & giving a final rinse with apple cider
vinegar diluted with water
. Exclude dandruff with consultation of skin specialist & get specific
treatment if needed.
* So avoiding exposure to heat or UV rays/ treatment of heat sensitivity with consultation of Allergy specialist & good & regular hair care would help you to get relief from the scalp itching.
I think the answer would provide you necessary information & be useful in finding the way out.Any follow up query is welcome.
Thanks.

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