Medscape reports that as more states move to legalize marijuana, allergies to the plant’s pollen are on the rise.

Cannabis sativa is a weed and it causes reactions just like any other pollen allergy,” said William Silvers, MD, from the University of Colorado School of Medicine in Aurora.

Silvers’ clinic began to see people with allergic reactions to the plant after the increase in direct exposure that accompanied the legalization of recreational marijuana in Colorado. For people with allergic tendencies, first- and second-hand exposure to C. sativa will increase “classic responses,” such as allergic rhinitis, sneezing, wheezing, itching, and asthma, he told Medscape Medical News.

Smoking the weed, direct exposure to the plant, contact with others who have touched plants, and breathing air in a grow operation “can all cause reactions,” he said. “And the more exposure they had, the greater the reaction, especially those who have allergic tendency,” he said.

The type of exposure to C. sativa is also a factor. Smoking the plant can induce typical allergic responses, the ingestion of hemp seed has been known to induce anaphylaxis, and “working with the plant can lead to dermatitis or contact urticaria,” he explained.