Start by wetting your hair thoroughly with lukewarm water. Warm water helps open the hair cuticle enough for cleansing, but very hot water can irritate a sensitive scalp and increase dryness.
Pour a small amount of shampoo into your palm — about the size of a coin is usually enough for short to medium hair, and a little more for very long or thick hair. Rub it between your hands, then apply to the scalp and roots. Massage gently with your fingertips in small circular motions. Avoid using your nails or scrubbing hard, because friction can aggravate a reactive scalp.
Let the lather work briefly, then rinse thoroughly. Leftover shampoo residue can itself cause itching or flaking, so take an extra moment to rinse the scalp and hair well.
If your hair is long, porous, or prone to tangling, follow with a light conditioner applied only to the lengths and ends. Keeping conditioner away from the scalp helps avoid extra buildup where the shampoo is doing its main work.
For a very reactive scalp, patch-test the shampoo on a small area of skin before your first full wash. Stop using it if you notice redness, itching, or any other irritation. If you have a scalp condition or are under medical care, it is sensible to ask a specialist before introducing a new product.