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Looks like your daughter has developed a lesion of Vector dermatitis or folliculitis
Vector (Paederus) dermatitis is a peculiar, irritant contact dermatitis
characterized by a sudden onset of red lesions on exposed areas of the body. The disease is provoked by an insect belonging to the genus Paederus.
Now firstly i would advise you to keep the area clean and dry as much as possible.
Do not apply any kind of moisturizing creams/lotions or oil over the affected area.
Wear cotton clothes so as to decrease the amount of sweating.
Clean the area with lukewarm water twice a day and apply an antibiotic cream like mupirocin
gel over the area twice daily.
Give oral antihistamine like levocetrizine once a day to decrease the swelling
If inspite of the above measures, the lesion persists or continues to increase in size, then your daughter might need a course of oral antibiotics
along with pain killers..In that case, i would advise you to visit a dermatologist
for proper assessment and treatment
Hope it helps
Wishing your daughter speedy recovery
Dr Geetika Paul