The same "venom shots" used to treat severe insect allergies may take the sting out of milder reactions as well, a preliminary study suggests.

The treatment, known as venom immunotherapy, involves a series of shots, given over months to years, that expose an allergy sufferer to gradually increasing doses of insect venom. This trains the immune system to build a tolerance to the allergy-provoking substance, so it doesn't over-react and cause severe problems.

Immunotherapy has long been given to people who suffer potentially life-threatening reactions to stings from bees, wasps and other insects.

However, many people have milder allergic reactions that, while not dangerous, are significant. Known as large local reactions, these allergies cause pain and extensive areas of swelling that can reach the size of a football.

"We just didn't know if venom therapy would work or cause problems for these patients," Dr. David Golden of Johns Hopkins University in Baltimore, the lead researcher on the new study, said in a news release from the university.

To study the question, Golden and his colleagues followed 29 adults with a history of large local reactions to insect stings — most of whom were frequently exposed due to outdoor jobs or hobbies.

The researchers treated 19 of the study participants with venom immunotherapy for seven to 11 weeks, while the rest went untreated.

Over the course of therapy, treated patients saw the size and duration of their sting reactions decrease by about half, on average, the researchers report in the Journal of Allergy and Clinical Immunology.

After the initial study period, all participants were given venom immunotherapy for up to four years. By year four, patients were seeing a 60 percent reduction in the size of their sting reactions, and a 70 percent drop in the duration.

The therapy did vary in its effectiveness, however. It nearly eliminated allergic reactions in some patients, but led to only moderate improvements in some others.

The reasons for this are unclear, according to Golden's team. But the preliminary success of the therapy warrants a larger study, they say.

"We believe these results will lead to broadening the guidelines for using venom therapy," Golden said.