A rash can be a sign of leukemia, a cancer of the blood that originates in the bone marrow, according to Healthline. Other signs of leukemia include inexplicable fatigue or weight loss, fever or chills, nocturnal sweating and frequent nosebleeds.
People with leukemia may have tiny red spots on their skin called petechiae, explains Healthline. These red spots develop when capillaries beneath the skin break. Due to the disease, the body does not produce enough platelets to seal these broken blood vessels, and this causes the red spots on the skin.
Dark-colored spots that resemble a rash can appear on people who have a form of leukemia called acute myelogenous leukemia, notes Healthline. AML affects children, and may also cause swollen or bleeding gums. Lumps, called chloroma or granulocytic sarcoma, may appear in the skin as well.