A Stranger Filmed Her on the Train. TikTok Users Decided She Had Monkeypox.

Lilly Simon, a 33-year-old in Brooklyn, does not have monkeypox. She does have neurofibromatosis type 1, a genetic condition that causes tumors to grow at her nerve endings. Those tumors were filmed surreptitiously by a TikTok user while Ms. Simon was riding the subway on a Thursday in late July during her commute.

In the video, Ms. Simon is sitting on the train wearing shorts, a T-shirt and a leaf-patterned mask. She is looking at her cellphone, unaware she is being recorded.

The video was later posted to TikTok with a monkey emoji and a question mark laid on top, appearing to indicate Ms. Simon might be riding the subway with an active case of monkeypox, the virus recently declared a global health emergency by the World Health Organization.

A few days later, Ms. Simon’s sister called her. She had seen the video. “Some of her friends had reached out to her,” Ms. Simon said. She said the news hit her “like a pile of bricks.”

“I’m not new to people being mean to the condition,” said Ms. Simon, who is a project manager and who used to work for the School of The New York Times, an educational program that is part of The New York Times Company. “I’ve had it since I was a child.” She said that with the recent spike in monkeypox cases, she’d thought something like this was “inevitable.”

One of the common symptoms of monkeypox is a painful rash that turns into raised pustules that eventually scab over and fall off as the virus runs its course. While most people who contract the virus will develop pustules, experts say there may only be a single lesion or the pustules will be localized to a person’s genitals.

In the TikTok video, the person recording zooms in on Ms. Simon’s arms, legs and ankles, where her small tumors appear as raised bumps on her skin. As a child, Ms. Simon said she was called a “leper” and her elementary school classmates would joke about her having smallpox.

She initially weighed whether or not to respond. “My heart dropped and all of a sudden I had to decide,” Ms. Simon said. “Do I, like, fight it? There’s no hiding that it’s me. Or do I, like, how should I respond to it?”

Ultimately, she decided to stitch her response to the initial video. (On TikTok, to stitch a video means to add your new video to an existing clip on the app. In this case, viewers can see a few seconds of the original subway video before Ms. Simon appears onscreen and tells the whole story.)

“I wouldn’t let something like that go,” Ms. Simon said of her choice. “I can’t look like a coward, and I’d rather stand up for myself than just let it pass.”

“The tumors are benign, but they are still all over my skin and give me a lot of health complications, both physical and mental,” Ms. Simon says in her video. Speaking with The New York Times, Ms. Simon added that she was diagnosed at…