Hawaii doctors are seeing more residents suffering from allergies and asthma because thick vog is aggravating their ailments.

"It’s been real busy," said Dr. Jeffrey Kam, chief of the Department of Allergy, Asthma and Immunology at Straub Clinic & Hospital.

He estimates a 20 percent increase in calls from his regular patients during the past two weeks.

"More people have been coughing a lot," he said. "People are having more asthma problems." A lot more residents are also complaining of burning and itchy eyes.

"I attribute all that to the vog," said Kam.

The end could be in sight, however.

Forecaster Peter Donaldson of the National Weather Service predicted the dense haze will subside by this Memorial Day weekend. The tradewinds, which blow vog southwest and away from Hawaii, returned Thursday and are expected to strengthen over the next few days.

Vog, short for "volcanic fog," is visible haze comprising gas and aerosols of tiny particles and acidic droplets that form when sulfur dioxide and other gases emitted from Kilauea Volcano interact with sunlight, oxygen, moisture and dust, according to the Hawaiian Volcano Observatory website.

The latest sulfur dioxide emission rate at Hale­mau­mau Crater and Puu Oo is more than 1,000 metric tons per day — 300 metric tons at Puu Oo and at least 700 metric tons at Hale­mau­mau, enough to fill up 50 Goodyear blimps, said Jeff Sutton, a geochemist with the U.S. Geological Survey.

Kilauea Volcano is the nation’s largest stationary source of sulfur dioxide, a colorless gas that has a biting, choking odor similar to fireworks or a freshly lit match, said Sutton. The emission rate is more than twice the amount of the most polluting coal-fired power plant on the mainland, he added.

Kam said many of his patients have increased their medication dose to relieve or prevent their symptoms from worsening.

"You have to have a game plan to increase certain medications so you don’t have to go to the ER," he said.

But breathing isn’t the only problem.

In the past few weeks, sulfuric acid droplets in the vog have caused a lot of damage to vegetation in Volcano Village, three miles from Hale­mau­mau, according to the observatory website. When vog mixes with moisture on plant leaves, it can cause severe chemical burns.

Despite the vog, the state Department of Health’s air-monitoring stations Thursday afternoon indicated air quality index levels across the state were either "moderate" or "good."

Locations that fall under the moderate category means some pollutants might be a moderate health concern for a small number of people who are sensitive to air pollution, according to the AIRNow.gov website, which reports the daily air quality in each state. Sites listed as "good" pose little to no health risk.