Hi Kai Sen
What you've described is an extremely common process called lichenification, which occurs after repeated scratching of the same area of skin. The part that has been scratched tends to thicken up and can become almost leathery in texture, and will often become more pigmented and brown.
It is very important that you get treatment for the cause of the underlying itchy process and try not to scratch the same area repeatedly.
This is because if the scratching does not stop, the skin will continue to thicken up further, resulting in a condition called Lichen Simplex Chronicus (LSC) .
This tends to be slightly harder to treat as LSC tends to be very itchy spontaneously or with minimal provocation, and creates a cycle of itching and scratching that is difficult to break.
I hope that you find this information helpful
Regards
Wei Sheng
Dermatologist