Just an example of the Internet problem of too much information and not enough context.
Many anti-vaxxers, adorable little child-endangering lunatics that they are, love to point out the ingredients in vaccines to show how dangerous they are to living creatures. The list generally includes formaldehyde, which is used in some vaccines to kill any antigens.
FORMALDEHYDE OMG WTF THAT'S THE STUFF THEY USE TO PRESERVE CORPSES AND IT CAUSES CANCER WTFBBQ!
Sure, it can cause cancer. As can most ingredients of everything, everywhere. And only at certain amounts of consumption that you are very unlikely to be exposed to unless you are... well, already a corpse.
The problem is that people already have formaldehyde in their bodies: in fact, your OWN BODY produces formaldehyde, and uses it to synthesize DNA, among other things. And formaldehyde enters our bodies through the food and liquids we eat, and the air we breathe.
So it's a matter of quantity then, since the body needs a small amount itself, and too much of it will kill you. So it must be the case that the vaccines have a quantity that could be considered dangerous, right!
YES! IN FACT, IT'S ALMOST AS DANGEROUS AS EATING A QUARTER OF AN APPLE! AND IT'S ALMOST AS MUCH FORMALDEHYDE AS YOUR OWN BODY PRODUCES FOR ITS OWN PURPOSES EVERY HALF OF A SECOND!
So keep that in mind: when anti-vaxxers warn you about the dangers of ingredients in vaccines, they are really warning you about something that results in less formaldehyde in your body than what is produced from the amount that ends up in your bloodstream from metabolizing the alcohol on the wipe the nice nurse uses to clean your arm. And less than what you would get from eating a nice healthy apple. And less than what your own body produces thousands of times a day.
THE MORE YOU KNOW.