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 the age of 8, has undergone multiple surgeries and has tumors growing in her brain and eyes. There currently is no cure for neurofibromatosis type 1. It is not contagious.

Ms. Simon said those complications also include scoliosis, which she was able to get “under control” through activities like yoga, sports and stretching, and several tumors growing inside her ears, which affect her hearing.

The tumors can be itchy and painful, and she often needs regular visits to her doctors. “Dealing with the general public with it has caused, like, some sort of, like, anxiety and depression and a little PTSD, and this situation definitely didn’t help,” Ms. Simon said, noting that she has “very much a mild version” and is in the “early stages” of the condition.

“I will not let any of y’all reverse any years of therapy and healing that I had to endure to deal with the condition and, of course, to exist around people like you,” she says in her TikTok. Ms. Simon said she chose to use “buzzwords” to make her plight relatable. “I knew people would resonate with it no matter what they’re going through,” she said.

Her response video has been viewed over one million times on TikTok. The original TikTok video has since been removed, but not before it had amassed a significant number of views. (It is unclear if the original video was removed by TikTok or by the original poster.)

Social media platforms like TikTok are something of a Hydra. Cut off one head and three more grow back. Or, in this case, delete one video and multiple reposted versions will appear in its stead.

Before its removal, the original video initially had commenting turned on, meaning anyone with a TikTok account could weigh in on the video. The comments, Ms. Simon said, ranged from genuine concern to threats of physical violence against her. TikTok did not respond to a request for comment for this article.

It is legal to record videos like the one of Ms. Simon, said Mickey Osterreicher, the general counsel for the National Press Photographers Association. “When you’re out in public, there is no reasonable expectation of privacy. It’s how we distinguish, you know, what’s public and what’s private,” he said. “When you’re in your home, that’s when you have the greatest expectation of privacy.”

He noted that privacy laws vary by state and emphasized that New York “probably has less privacy than other states depending on what you’re filming for.”

What a person does with a recording after taking it, however, can change the situation. “The thing that I tell folks all the time is that it’s a completely different bundle of rights when you use a picture and you do something that might be defamatory or hold someone up to false light,” Mr. Osterreicher said.

“I think, you know, the fact that this person recorded it, that was fine,” he said. “But what they did with it afterwards, she might have a very sound cause of action against that person for doing what they did.”

Having monkeypox, or even being believed to have monkeypox, can come at an emotional cost. “People are afraid to have it associated with them because of social stigma, ostracization and assumptions made about their sexual or intimate lives,” said Alexander Borsa, a doctoral student in sociomedical sciences at Columbia University and a researcher with the Harvard GenderSci Lab. Mr. Borsa has also been part of a New York City Department of Health and Mental Hygiene working group dealing with monkeypox.

Mr. Borsa highlighted how some TikTok videos, such as those from people speaking in detail about what it is like to have monkeypox, could be a positive use of the app. But he also noted it was not surprising to see the platform being weaponized in this way, as many L.G.B.T.Q. people seek guidance and treatment information online.

For now, at least, Ms. Simon’s response video is the one demanding the attention of TikTok’s fickle algorithm, and she has since heard from a number of strangers whose lives have also been affected by neurofibromatosis type 1.

“I don’t think I would have ever honestly put myself out there like that to find those people otherwise. It is isolating, and there’s not a lot of people to talk to about it, especially, like, you know, in front of me, at least, or at least in my community and in the places, the spaces that I occupy,” Ms. Simon said of her condition. “I don’t really even talk to my friends about it. So again, for these strangers out of nowhere, it kind of, it did feel … that part felt OK.”

In order to send a direct message on TikTok, both parties must follow each other. The person who posted the original video has since followed her TikTok account, Ms. Simon said, but she is uninterested in reciprocating. “I would have said exactly what I said in the video,” Ms. Simon said of the two potentially connecting.