Psoriasis (pictured left) of the scalp is commonly seen, and might be the only place that you experience psoriasis. Psoriasis ranges from pink areas covered in silvery scale which bleeds when picked, to a severe form called pityriasis amiantacea with thick adherent scales which bind several hairs together.
Pityriasis capitis (dandruff) and seborrhoeic dermatitis (eczema) are caused by excess sebum on the scalp and a yeast called Malassezia, these conditions are characterised by greasy, yellowish scales of skin.
Itching of the scalp is often caused by a reaction to hair products, this can be mild reactions from a product being left on too long, or from an allergic reaction to a specific ingredient. Itching can also be related to some hair loss conditions, or may have no identifiable cause.
Seborrheoa oleosa is the technical term for a greasy scalp, which is caused by overproduction of sebum from the sebaceous glands. While some amount of sebum is important for the health of the scalp, an excessively greasy scalp can be a sign of a hormone imbalance or dietary issues.
Acne can affect the scalp, just as it affects the face. An overproduction of sebum causes a blockage in the hair follicle, leading to bacteria multiplying and infecting the tissues. Some forms of scalp acne can be intensely itchy, and leave small scarring areas of hair loss.