NEW YORK (Reuters Health) - The incidence of reddish skin tumours called infantile hemangiomas has grown in recent years, and low birth weight is the leading risk factor driving the increase, new research suggests.

"If we can identify certain factors that put infants at risk for hemangiomas, that helps us understand how to prevent or treat them more appropriately," study chief Dr. Beth A. Drolet, from the Medical College of Wisconsin in Milwaukee, told Reuters Health.

Infantile hemangiomas are non-cancerous tumours that can grow rapidly during infancy, but usually resolve by 9 years of age. Hemangiomas are the most common tumours in infants and, aside from cosmetic concerns, most have no medical significance. However, some may cause medical problems or permanent scarring, Drolet and her colleagues point out in the Journal of Pediatrics.

To elucidate features influencing the development of infantile hemangioma, the researchers studied 420 children with infantile hemangioma and 353 control children.

Their study confirmed several recognized risk factors, including female sex, Caucasian race, and preterm birth. However, they report, being born at a low birth weight rather than being born prematurely per se is "the most significant risk factor for developing infantile hemangioma."

For every 500-gram decrease in birth weight, the likelihood of the birthmark rose by 40 percent.

Genetics may also play a role, according to the researchers. In their study, children with infantile hemangioma were twice as likely as children without hemangioma to have an affected mother or other close relative (33 percent versus 15 percent).

Knowledge of contributing factors should lead to better interventions, Drolet noted.