Despite a superficial resemblance to blood blisters, nodular melanomas continue to grow after two to three weeks, warns the Melanoma Education Foundation. Melanomas occur in locations without injury, while blood blisters are usually the result of damaged blood vessels or skin tissue.
Blood blisters can typically be treated at home but can also heal on their own. To avoid chances of infection, they should never be popped. Accompanying pain can be treated with an ice pack applied for 10 to 30 minutes to the affected area.
Nodular melanomas occur spontaneously, according to the Melanoma Education Foundation. They are dome-shaped and appear black, blue-black, dark brown or brown-red over time. However, in some cases melanomas can be pink, grey or light to medium brown, or remain flesh-toned. Nodular melanomas can spread rapidly beneath the skin, sometimes in as little as three months. They account for roughly 15 percent of all melanoma cases in the United States.
Nodular melanomas can appear anywhere on the body, warns SkinCancerNet. They are a very aggressive type of melanoma that can sometimes avoid detection because they do not expand across the skin as rapidly as they penetrate beneath it. Although they can appear on a pre-existing mole, they often appear on clear skin.