Itchy rash on back of neck and in hairline also on lower back?

Itchy back: You might be allergic to your shampoo or another hair care product. Without a medical exam it would be difficult to say. Consider using only a non sensitizing shampoo such as free and clear and avoid other treatments. If that doesn't work seek out a board certified allergist or dermatologist.

Have it evaluated.: There are many types and causes of skin rashes. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.