Hi,
An allergy usually refers to a reaction by our immune system in response to certain allergens.The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. If you do not have other signs or symptoms present, his rules out allergic causes. Your condition could be due to skin disorders, fungal infection, stress or head louse.
This could be due to contact dermatitis if there is a rash present with the itch. The main causes of contact dermatitis could be a new shampoo, soap, hair dye or hair product, mainly if the product has alcohol in it.
It could also be due to seborrheic dermatitis or dandruff. Tinea capitis is another differential which could be diagnosed with the skin scrapings evaluated under the microscope.
Head lice is another common cause of itchy scalps which can easily spread with close contact. Stress is another factor that is a possible cause of your condition.Make sure that you rinse all shampoo residues in your hair. If you have tried many types of shampoo or conditioner and did not help, it is best to see your doctor for further evaluation of your scalp and proper management.
Take care and keep us posted.