Diagnosis is primarily visual, based on a dermatologist's examination of the spot's appearance: its flat, brown, or black color; its well-defined borders; and its typical location on sun-exposed skin. While a biopsy might be performed in rare cases to rule out other skin conditions that might resemble age spots, it's usually not necessary for diagnosis. The doctor will consider your medical history, including sun exposure, and conduct a visual assessment to confirm the diagnosis of age spots. Diagnosing age spots may include:

• Visual inspection. Your doctor can diagnose age spots by visually inspecting your skin.
• Skin biopsy. If there's any doubt, your doctor may do other tests, such as a skin biopsy. During a skin biopsy, your doctor takes a small sample of your skin (biopsy) for microscopic analysis. A skin biopsy is usually done in a doctor's office using a local anesthetic.

Other conditions 
Other conditions that can look similar to age spots include:

• Moles. Although they often appear as small, dark brown spots, moles (nevi) vary in color and size. They can be raised or flat and can develop almost anywhere on your body — even between your fingers and toes.
• Seborrheic keratoses. These tan, brown or black growths have a wart-like or waxy, pasted-on appearance and range in size from very small to more than 1 inch (2.5 centimeters) across.
• Lentigo maligna. One type of skin cancer known as lentigo maligna melanoma can develop in areas of long-term sun exposure. Lentigo maligna starts as tan, brown or black lesions that slowly darken and enlarge. They tend to have an irregular border and uneven coloring and may be slightly raised.