A pyogenic granuloma is a harmless overgrowth of large numbers of tiny blood vessels on the skin. It carries no risk of cancer; they are not an infection.
Most pyogenic granulomas come up for no obvious reason, but some seem to follow minor damage to the skin, such as a cut that does not heal properly or a prick from a thorn. They can occur at any age, but are most common in children and young adults.
During pregnancy they can come up inside the mouth. Some medications can induce multiple of these lesions, they can appear on skin vascular malformations (birth marks).