I have brown spots on my neck and back. What can it be?

Doctor can evaluate. Spots can be due to allergic, viral, or fungal causes. Sometimes spots are sensitive skin eczema, or due to aging or sun exposure. A primary care doctor or a dermatologist (skin doctor) should look at it if it doesn't go away, or it worsens, with simple treatment. Simple treatment of an itchy spot means trying over-the-counter Hydrocortisone 1% cream three-times-a-day for about 5 days.