Obligatory this happened many years ago.
Starting in middle school, I went on a self-exploratory journey of doing as much crazy shit to my hair as humanly possible. I was a baby gay at the time and loved seeing all the out and proud people online who colored their hair or had fun hairstyles. At 14, I finally managed to convince my mom to let me cut my hair short and dye it fun colors.
Cut to my sophomore year of high school. At this point, I'd dyed my hair dozens of times. After the first few times getting it done by a professional, my mom took over doing the process for me. I'd sit at the kitchen table with a little plastic cape on and she'd meticulously apply whatever color I'd picked out at the drugstore. We did this every few months, and yes, we'd bleach my hair every time. I have brown hair, so there was no way I'd have the vibrant colors I wanted without bleaching it. By the time this story starts, my mom was very worried about the health of my hair after bleaching it so many times. I personally didn't care as long as my hair was a fun color, but I wasn't about to pick a fight with her over this.
So, in the spring of my sophomore year of high school, I wanted to dye my hair blue. My mom told me that she was going to a hair supply store to see if they had any more natural hair lightening products to use to avoid damaging my hair further. Again, I didn't care as long as my hair was dyed. That night, we sat down to get the process started and she pulls out the supplies she got at the store. The hair lightener she found was supposedly "all natural" and she started applying it to my hair.
It didn't take long for the smell to hit us. My younger sister, who was in an adjoining room, even walked in to where we were to find out what the source of the smell was. It was pungent, reminiscent of rotting eggs, and the smell was coming from the hair lightener. It smelled gross in the moment, but I figured it was a small price to pay so my mom would keep letting me color my hair. We ended up having to use the lightener twice in order to get my hair to the right color so the blue would be vibrant enough. My mom applied the blue hair color and I put on a shower cap to let it sit for a couple hours.
After the processing time for the color was done, I hopped in the shower to rinse it off (yes, I know hair color can stain porcelain, it was just the easiest way and I was a teenager). At that point, the smell had been gone since I last rinsed out the hair lightener. I figured I didn't have to worry about the smell ever again. Then, as I was rinsing out the hair color, the distinct smell of rotting eggs returned. I was struck with the realization that my hair started stinking because it had gotten wet. The hair lightener my mom was so insistent on using had cursed me with stinky hair.
After the initial horror had worn off, I figured it wouldn't be too bad. I mean, how often would my hair be getting wet outside of showering? No one should ever find out about this, right?
The next day at school, I had gym. We had two different kinds of gym class at my high school, competitive sports and what was called "lifestyle fitness". I took the latter, and the class was usually chill. We often did yoga or had free time to use the various pieces of equipment the school had in a small room. That day, it was just my luck that we were doing aerobics. If you don't know, that's the kind of exercise where you step up and down on a block. If you've never done it before, it's a lot more intense than it seems. By the halfway point of class, I had built up quite a sweat. And that's when I noticed it: the smell of rotten eggs.
I start to silently panic. I had not anticipated that sweat might activate my hair to start stinking. I had no way of drying my hair following gym class, no hair dryer or towel I could use. All I could do was pray that no one noticed or brought it up.
After gym, I had AP Chemistry. This is where my true fuck up began.
My assigned seat was right in front of the teacher's desk. My teacher, "Mr. J", was a super chill guy, genuinely one of the best teachers I've ever had. I sit down, continuing to pray that no one noticed the rancid scent coming off of my hair. Everything seemed fine for the first few minutes of class. My classmates trickled in, taking their seats and getting ready for the lesson.
About five minutes after Mr. J starts teaching, he stops and asks the class, "Do you smell that?"
My heart starts pounding. The entire class starts nodding, agreeing that there was a weird smell and trying to identify it. Now, if you don't know, the smell of rotten eggs is associated with the element sulfur, a substance that is known to be toxic in many of its chemical forms. And I was now sitting in a science lab in a high school with the scent of a potentially dangerous chemical emanating from my hair.
All I could do was sit still and stare into the ether. I hoped that if I said nothing, Mr. J would just move on with the lesson and spare me the humiliation of having to explain that it was me that was stinking up his classroom. To my horror, Mr. J began walking around the classroom, sniffing in order to find the potential source of the smell. He went from corner to corner, and was able to smell my hair from about thirty or forty feet away. The scent had permeated the entire classroom. I kept getting redder by the second.
To make matters worse, one of my classmates who was in my gym class the previous period raised her hand and said, "I could smell it in the gym too. They were doing construction outside, so that's where I thought the smell was coming from."
Fuck my fucking life. Someone had smelled my hair in the gym, and now this had become a school-wide issue because it appeared that potential sulfuric fumes were permeating the whole building and could put the lives of hundreds of children at risk. Mr. J went into the adjacent classroom to ask that teacher if she was performing some sort of experiment that day. Of course she wasn't. No one was doing experiments that included sulfur (except my mother, apparently).
Mr. J came back into the classroom and tried to continue the lesson. For a moment, I thought I was in the clear. My face was still red-hot, but I thought I had potentially adverted having to give myself up as the culprit. But of course, it was not to be. No less than ten minutes later, Mr. J went for the classroom phone to call the front office and report the concerning smell.
That was the last straw, the push I needed to open my damn mouth and come clean. I quickly spoke up, telling Mr. J he didn't need to call the office because the sulfur smell was coming from my hair. I explained about the hair lightener, about being in the same gym class as the other student, and about the smell happening when my hair got wet. It was a short explanation, and Mr. J was relieved and understanding that I was anxious about speaking up. The class moved on quickly afterwards, and no one at school ever brought the incident up later as far as I know. I moved schools after that year, so I have no idea if the story stuck around.
I told my mom what happened when I got home, and she apologized profusely. We never used that lightener again, and thankfully, the residual smell washed out of my hair soon after. I stopped regularly dyeing my hair after I went to college, and I moved on to shaving my head completely, before eventually finding a style I love and have stuck with ever since.
TL;DR: In high school, my mom used an "all natural" lightener instead of bleach to dye my hair, which smelled of rotten eggs when it got wet. The next day, I had gym class right before chemistry, my hair got wet from sweat, and my chemistry teacher almost called the front office because he thought there was a sulfur gas leak in the school.