As the federal government inches closer to legalizing recreational marijuana, doctors are warning of an emerging health hazard: cannabis allergies.

“The more people that are exposed to marijuana, the more likely we are to see allergies,” Toronto-based allergist and immunologist Dr. Gordon Sussman told CTV News. “Marijuana allergy can potentially be very severe -- potentially, it can cause life-threatening reactions just like a peanut allergy.”

One of Dr. Sussman’s patients is Doneil Oliphant, who learned the hard way that he had a marijuana allergy when he touched his face after handling cannabis oil.

“My eyes were swollen (almost) completely shut,” Oliphant recalled. “You could barely recognize me -- my face got a very round look to it.”

The symptoms lasted several hours, Oliphant said. Soon after, he found himself taking a skin allergy test at Dr. Sussman’s office and was shocked to learn that he was allergic to weed.

“I didn’t even know it was possible,” Oliphant said. “Marijuana allergies (are) not something you hear about very often and so I was actually pretty surprised that I had one.”

With marijuana use becoming more and more prevalent, Dr. Sussman says he’s seen an increasing number of patients test positive for cannabis allergies over the past 10 years. Symptoms, he says, can range from skin irritation to respiratory issues to -- in the most severe cases -- full-on anaphylactic shock.

“Skin symptoms are generally from touching it,” Dr. Sussman explained. “You can sometimes see itchy skin and hives and you can sometimes see swelling of the eye if you touch your eye after touching the marijuana plant. Respiratory symptoms can be nasal running and sneezing with associated itchy, watery eyes. Occasionally you’ll see wheezing, shortness of breath and asthmatic reactions. Anaphylactic symptoms generally occur with hempseed (or eating marijuana products)… Potentially, any anaphylactic event can be serious and life-threatening.”

One former undercover officer with the Ontario Provincial Police told CTV News that she didn’t know she had a potentially deadly cannabis allergy until she first touched the plants while on the job.

“We were doing drug eradication, so we were pulling marijuana plants from a field,” the woman, who asked not to be identified, said. “I had a reaction to the plants which I’d never had before and my hands and forearms swelled and I got a really bad rash on them and really bad swelling… I wound up having to go to (an emergency room) because the swelling and the rash was so bad that I actually couldn’t use my hands.”

Even inhaling second-hand marijuana smoke has sent her to hospital.

“What happens is I get this really sharp pain behind my left eye, it’s excruciatingly painful and it’s just like a hot poker in my eye, and then my chest starts to tighten and my face gets all tingly and my arms and hands and extremities tingle and it feels like there’s just a vice in my chest where I can’t breathe,” she said. “It’s quite scary.”

Now, carrying an EpiPen wherever she goes, the woman worries about being increasingly exposed to marijuana smoke once pot becomes legal.

“I’m not able to go to concerts,” she lamented. “And once it’s legalized, I’m afraid (of) even just walking down the street.”

Like most allergies, the only truly effective way to deal with a marijuana allergy is avoidance, Dr. Sussman says.

With legalization on the horizon, Dr. Sussman has also launched the first Canadian study to see how many people have undiagnosed marijuana sensitivities. His goal is to better prepare patients and doctors -- and even potentially save lives.

“If you look at a study done out of Colorado, about 10 per cent of people just with passive exposure (to marijuana) did have sensitization or allergy symptoms,” he said. “At this point, it’s under-recognized and under-diagnosed.”

With files from CTV News’ medical affairs specialist Avis Favaro and producer Elizabeth St. Philip