I get asked this a lot, what is the secret with Thai spices and seasonings. Well, there are no secrets or hidden ingredients. Thai cooking is very basic, and when you think about it, it is as simple as boiling water, adding meat, vegetables, and spices, that is it for a soup, add chili paste for a curry.
Basic spices or seasonings used are:
Whole chilis (normally Birds Eye Chilis, everyone grows them)
Shallots (the tiny purple onions)
That is pretty much it, now to add to that, they use a few things that are not healthy, by any means. First is MSG, used in nearly everything cooked, me, I hate it and I have to keep an eye on what I am cooking or I get it added. Then there is palm oil, absolutely the most worthless cooking oil ever made. If a Thai is cooking, they are using palm oil. When I got here and bought olive oil, people looked at me like I was on crack, I use olive oil, or real butter, or both together. Olive oil is not cheap, palm oil is dirt cheap so Thais use that. One bottle of olive oil can be a days salary for most folks.
To increase the heat of the dish, add more chilis, as simple as that. No secrets, no special ingredients. Thai food is good, easy to prepare, and healthy.