system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Are there primary scents just like there are primary colors?

I was thinking of an app idea that has a hardware attached scent dispenser. This way, I can send a scent for my friends to smell across the country. However, to accomplish this I thought that perhaps there are ways to create any scent just like you can create any colors using primary colors.
gpt
Well, there's good news and bad news.

The good news is that, *yes*, just as your eyes have a limited variety of cones in them and infer other colors based on how those colors activate combinations of cones, your nose has a limited variety of olfactory receptors in it and infers other odors based on how those odors activate combinations of olfactory receptors.

The bad news is that while there are only 3 types of cones in our eyes, our best guess for the number of types of olfactory receptors in our noses is "about 400".

For each of those 400 different types of receptors, you'd need to find a chemical that activates that one and mostly doesn't activate any of the others.  There's no guarantee that such chemicals will exist in all cases, so you'll probably end up needing more than 400.  (For example, if you can't find a chemical that activates "only receptor #298" then you may need one that activates "only receptors #1 and #298", another that activates "only receptors #2 and #298", and so on.)