pheromones

Good question, and I don't have a ready answer.

All your senses become heightened.....you have to restrain yourself from reaching out and "touching" that individual. And, yes - the pheromones. There simply is no mistaking it for anything else....

a positive reaction to a potential significant other

For me chemistry is just emotional or sexual compatibility. It’s important but not necessary for a relationship.

To me it's all of the things which describe how my body reacts to theirs. Not any conscious reaction, but the autonomous systems my body. When I touch them do I feel an electric tingle in my fingertips? When they touch me does my skin respond by becoming hyper sensitive? When they move with me either walking or dancing together can I feel my body react to theirs? When I'm close does the smell of their skin and sweat appeal to me? When we kiss do I get lost in the taste of their lips, tongue, and mouth?

I can get a good feeling of liking someone online. We can have the most intimate conversations and agree on everything that makes us happy. I don't think that is "chemistry" that's intellectual compatibility. All of that can be true but if we meet and it feels at all awkward, then we don't have chemistry.

I have no definition.I knows it when l feels it.

For me it is when my body responds to someone, almost without me being aware of it at first, and certainly without my intention. That response may or may not coincide with an emotional or mental attraction. For instance, I have found myself physically attracted to people I actually despise from an ethical or political standpoint. That's a bit disturbing to say the least. But it also points out that our drive to reproduce is very fundamental to our natures, and won't be disrupted by factors as comparably subtle as social identity, at least in my experience.

You just know. It's physical, but it's beyond that too, it's emotional, mental. You just "get" each other.

I'm not sure. I noticed a couple of responses that included smell or kissing. That might be true in some cases. However, I've had chemistry with people I've never seen face to face. I think it's one of the great mysteries in this world.

An immediate strong physical attraction or liking..

Mixing Gin with Tonic