On April 16, a woman named Elise Nguyen shared disturbing images of second-and third-degree burns on her neck and wrists on her Facebook page. She says she had applied essential oils directly to the skin, went to a hot yoga class, then visited a tanning bed in order to avoid “frying her skin” before a trip to Jamaica.

Related: 7 Ways Dermatologists Protect Their Skin—Without Totally Avoiding The Sun

First things first: We probably don’t have to remind you that going to a tanning bed is one of the worst things you can do for your skin—and your overall health. To recap, tanning beds are a known carcinogen, increasing your risk of melanoma, the deadliest form of skin cancer, as well as nonmelanoma skin cancer, according to the American Academy of Dermatology.

For Nguyen, however, the combo of the tanning bed plus essential oils did some very immediate damage.

“The next day, I noticed irritation where I applied the oil,” she wrote on Facebook. At first, she thought it was a reaction to a new laundry detergent but over the next couple of days, she developed “nasty blisters due to a chemical burn.” “It’s been hell,” she says of her 22-day recovery.

Related: How to Check Yourself for Skin Cancer

“This is an unfortunate incident and a reminder for all of us to be careful about UV exposure,” says Lauren Ploch, M.D., a board-certified dermatologist and member of the American Academy of Dermatology. “The mostly likely scenario is that [Nguyen] developed either photoallergic dermatitis or phytophotodermatitis,” Ploch says. In photoallergic dermatitis, an adverse reaction occurs when a chemical becomes an allergen in the presence of UV light, while phytophotodermatitis occurs when certain photosensitizing compounds from vegetable or fruit products contact our skin before exposure to UV light.

See what a doc has to say about sun protection.

Any UV light (natural or artificial) can lead to these conditions, Ploch says, but since tanning bed light is more concentrated, it may lead to more severe reactions than natural light.

Applying essential oils directly to your skin is an appropriate way to use them topically, according to the essential oil brand she used. The problem? Exposing your skin to sunlight right after application is where things go wrong. The National Association for Holistic Aromatherapy offers a no-nonsense warning against using essential oils before exposure to UV rays, either from natural sunlight or indoor tanning. Doing so can result in skin pigmentation or burns, ranging from “mild color change to deep weeping burns,” the website states. To avoid this scary scenario, it’s best to stay out of the sun for at least 24 hours following application.

Related: This Woman’s Graphic Photos Expose The Painful Dangers Of Tanning

Nguyen admits she missed a warning label: “Turns out, there is a teeny tiny caution on the bottle that states ‘stay out of sunlight or UV rays for up to 12 hours after application,’” she says. She takes the blame in her case, but hopes that her experience helps others avoid making the same mistake.

Take this as a warning that even “natural” products need to be used safely—as well as yet another reminder to always avoid tanning beds, no matter what’s on your skin.