Chemists talk about amino acids in a few different ways, so the “right” number depends on what you mean by how many amino acids exist.

Core answer

  • In nature overall: more than 500 different amino acids have been identified.
  • In human (and most life) proteins: 20 standard “proteinogenic” amino acids are used routinely.
  • With special cases: 2 more, selenocysteine and pyrrolysine, are also genetically encoded in certain organisms, bringing that number to 22 in total.

So, depending on context, you will most often see:

  • “20 amino acids” → the standard set that build most proteins.
  • “21 amino acids” → standard 20 plus selenocysteine.
  • “22 amino acids” → standard 20 plus selenocysteine and pyrrolysine.

Quick Scoop

  • Hundreds of amino acids exist in nature (500+), but only a small subset go into building proteins in your body.
  • Your genetic code is effectively “hard‑wired” for 20 main building blocks, with special machinery that can add 1–2 extra in some species.
  • The confusion you see online (“18, 19, 20, 21, 22…”) usually comes from mixing:
    • proteinogenic vs. all amino acids in nature
    • essential vs. non‑essential amino acids for humans
    • whether selenocysteine and pyrrolysine are counted.

In forum discussions, people often argue “it’s 20” vs. “it’s 21 or 22,” but they’re usually just talking about different definitions, not different facts.

Simple takeaway

If you’re asking for everyday biology/biochemistry:

  • Say “20 amino acids” for the standard set that make up proteins.
  • Note that “22 amino acids” is also correct when including the two special genetically encoded ones, selenocysteine and pyrrolysine.

Information gathered from public forums or data available on the internet and portrayed here.