Potent Poison Ivy

An unusually moist spring and a hot summer have conspired to produce a particularly abundant crop of poison ivy this year, leaving more Massachusetts residents than usual scratching their skin raw.

Scientists believe the plant might also be gaining in potency because, especially in cities, it is thriving on increasing carbon dioxide levels, partly the result of burning fossil fuels and cutting down forests.

Landscapers in the region have reported an increase in house calls about poison ivy, whose clear, liquid oil causes telltale streaks of red skin, rashes, and blisters.

''It's everywhere. It's out in force,'' said William Bartlett of Bethlehem, Connecticut, who has removed poison ivy for more than 30 years around Connecticut and Western Massachusetts. ''I usually don't get busy until the beginning of June. I was busy since the 10th of April this year.''

The exact number of poison ivy cases is hard to track, because many people use over-the-counter creams and sprays to quell the scratching without ever making a trip to the doctor. But sales of ointments commonly used to treat poison ivy exposure have increased significantly, according to spokesmen for their manufacturers.

In Greater Boston, purchases of Tecnu Extreme Medicated Poison Ivy Scrub, which is available in every major drugstore chain, are 24 percent higher this year compared with last, with most of the increase over the past few months.

Zanfel Poison Ivy Wash, another widely available option, has seen a 40 percent increase in its Northeast retail sales relative to last summer. Given that there is minimal advertising in the poison ivy product industry, the large changes can be attributed mostly to a greater need for the treatments, said Steve Sisler, vice president of sales at Zanfel Laboratories Inc.