Aug. 8, 2017 -- When Rachael Armstrong first started using essential oils last year she, as she puts it, “dove right in.”

Each morning, she placed a drop of frankincense oil, which some say is an immune booster, under her tongue. If her head hurt, she dabbed calming peppermint oil on her temples. At night, she massaged the bottoms of her feet with grapefruit oil, often billed as an appetite suppressant. By day, she lathered her arms with antibacterial bergamot oil and dropped fragrant lemon oil into her detergent and water bottle.

Then one night after sitting in the sun at a baseball game, she spotted a rash on her neck and arms. By morning, her eyes were swollen shut and the oozing welts on her neck burned. The rash cleared. But for weeks, each time the sun hit her skin even briefly, it returned. Ultimately, it got so gruesome that doctors had to inject her with steroids. The suspected culprit: A toxic reaction to essential oils.

“I admit I was probably overusing them,” says the 44-year-old mother of five from Omaha, NE. “But I don’t think people are aware that even though they’re natural products, they can do real damage.”

Armstrong is among a small but growing number of consumers turning up with chemical burns, allergic reactions, respiratory issues, and other side effects from the popular aromatic plant extracts. In the past year, retail sales of essential oils soared 38%, with consumers spending more than $1 billion on oils and accessories, according to market research firm SPINS. That’s not including tens of millions in sales from companies that bypass retail shelves and sell directly to consumers via a growing network of independent distributors.

Those distributors, and more demand for over-the counter “natural” remedies free of the side effects that can come with prescription drugs, has fueled a surge in essential oils demand.

But as their DIY use explodes, concerns abound.

“There is definitely credible science behind certain benefits for certain essential oils,” says Cynthia Bailey, MD, a dermatologist in Sebastopol, CA. “But you have to choose wisely, and you cannot use them indiscriminately.”