But the famous fact that apples contain cyanide is not technically true. The chemical actually found in apple seeds is called amygdalin, which only turns into toxic hydrogen cyanide when it breaks down, that is, through digestion.
So how many apple seeds is a lethal dose? The good news is that accidentally eating a handful of apple seeds here or there probably won’t cause you much harm. The threshold for cyanide poisoning varies from person to person depending on body weight – not surprisingly, the higher the body weight, the higher the dose needed to cause bodily harm. However, it has been calculated that the average adult would need to ingest around 150 apple seeds – the contents of around 18 apples – to experience cyanide poisoning. Could you really ingest it in one sitting? Probably not.
But there’s another factor that plays into the likelihood of apple seeds causing you physical harm if eaten in excess: their hard shells. Like many other seeds, those of apples are virtually indigestible, so they would likely pass through the digestive system rather than release their chemicals into the bloodstream.