Humidity and heat will eventually get to books kept in warmer climates like Thailand's. The pages can turn brown or become brittle. But if the climate is hot and the humidity is very low, the binding will start to crack. It is better to keep the books in an airconditioned room. Don't turn the aircon on and off.
Paper is very susceptible to moisture.
When there is water in the air, paper absorbs it. When the moisture goes away, it will release water. All that absorption and releasing can cause damage. The acid from your hands will eventually do some damage. Wash and dry your hands or use soft cotton gloves.