"Paint thinner" covers a wide variety of solvents so you have to be more specific what's in the one you are asking about. Here is Wikipedia's listing of the solvents ued in various paint thinners:

"Products used as paint thinners include:

Mineral spirits
Acetone
Mineral turpentine (turps)
True turpentine
Naphtha
White spirit
Methyl ethyl ketone (MEK)
Dimethylformamide (DMF)
2-Butoxyethanol, or any of the other glycol ethers"