Thank you for the question. One of the commonest cause of itchy scalp is a form of eczema known as seborrhoeic eczema. The scalp can be red and sometime flaky and this often associated with scalp itch. This can be treated with a mild shampoo and a very mild steroid cream or lotion like hydrocortisone can be helpful.
There are of course other causes of scalp itch like head lice, which is much less common in Singapore.
If the rash is persistent, it is best to see your dermatologist/doctor to confirm the diagnosis and get the appropriate treatment.