Mostly it is due to allergies, like dust, smoke, pollen, chemicals, animals, or food. It can be due to the start of the infection.
If the itchy throat is accompanied by wheezing or breathing difficulty, then it is an emergency, and look at our emergency hospital locations.
Treatment is by avoiding allergens. You can try the counter antihistamine like Chlorpheniramine(sedative) or Cetrizine(non-sedative). Check with a doctor if it is getting worse or nonresponsive.