Radioactivity!
I was born in 1952. and had to watch all the post WW2 monster movies with my older brothers. I just knew that anything involving radium would turn me into a wart-ridden deformed monster in only a few hours.
At my 8th birthday party I was given an alarm clock as a gift, and it had those ominous little green bits around the numbers. Not wanting to be rude, I wrapped it in about three pairs of socks and a sweater or two, and stuck it WAY back in a dresser drawer, just to make sure that I wouldn't wake up with my lips sloughing off.
I think my Mom finally found it when we moved, about six years later.
A childhood belief about chemistry

others believed things like this
- When you lie your lips move or your eye turn green— Tanya
- I thought the boogey monster was a monster that ate boogers at night in front of youAnon
- I Used To Believe The Monster Beverage/Energy Drink Was Monster Milk!— KellGirl
- I would turn the lights off and then leg it up the stairs thinking a monster would be chasing me.Anon
- My mum told me that if you picked your nose and flicked it on the floor then it would turn into a monster!— MadMack
- I used to think the Static in the TV where millions of flying bugs stuck wanting to escapeAnon