If the affected skin doesn't improve or gets worse, it's time to call the pediatrician. He or she might simply suggest one of the medicated shampoos mentioned earlier, which are available over the counter. If you remember, products using ketoconazole, selenium and corticosteroids are used for severe cases, and some of them require an RX.
Another medicinal option the doctor might recommend is hydrocortisone cream. This is usually prescribed when the skin is inflamed or reddened. For cradle cap, a cream with just 0.5 to 1 percent hydrocortisone should work fine -- you can pick it up at the drugstore without a doctor visit. Hydrocortisone cream is the topical answer to all kinds of skin irritation from poison ivy to hemorrhoids, so you know it does an itch good. You can apply it a few times day to soothe discomfort and keep baby from scratching with those surprisingly sharp nails.