When you repeatedly scratch a mosquito bite on your arm, skin irritation is quite noticeable, but when you scratch an itchy head, your hair strands cover it up a bit more. Regardless, repeated and aggressive head scratching can cause damage to the scalp and hair follicles.
Scratching your itchy scalp can lead to scalp infections that can cause more itchiness and even pain. Fungus or bacteria can enter your scalp through damaged hair follicles or damaged skin created from scratching.
You could develop tinea capitis, also known as ringworm, which can cause red, scaly, bald patches that can spread anywhere on the scalp. When bacteria enter your body through a damaged hair follicle, it is called folliculitis.
Impetigo is a condition caused by staphylococcus that usually affects children and appears around the nose and mouth. It can appear as red sores on the scalp that leave a yellowish-brown crust on the skin after they burst.