Being a tropical country, Thailand has its fair share of exotic tropical diseases. Malaria is generally not a problem in any of the major tourist destinations, but is endemic in rural areas along the borders with Cambodia (including Ko Chang in Trat Province), Laos, and Myanmar. As is the case throughout Southeast Asia, dengue fever can be encountered just about anywhere, including the most modern cities. The only prevention is avoiding mosquito bites. Wear long pants and long sleeves at dusk in mosquito areas and use repellent (available at any corner shop or pharmacy).
Food hygiene levels in Thailand are reasonably high, and it's generally safe to eat at street markets and to drink any water offered to you in restaurants. Using common sense — e.g., avoiding the vendor who leaves raw meat sitting in the sun with flies buzzing around — and following the precautions listed in our article on travellers' diarrhea is still advisable.
The sun is harsher than at higher latitudes. A couple of hours in the sun with unprotected skin will result in redness and a painful night even on a cloudy day.
Thailand has a high rate of HIV . (Estimated adult (15-49) HIV prevalence is (1.3% of population in 2014)) and other sexually transmitted diseases are common, especially among sex workers. Condoms are sold in all convenience stores, supermarkets, pharmacies, etc. Avoid injection drug use.
There's a pharmacy on every block in Thailand and most are happy to sell you anything you want without a prescription. However, this is illegal, and police have been known to bust tourists occasionally for possessing medicines without a prescription, even innocuous stuff like asthma medication.
Thailand is a popular destination for medical tourism, and is particularly well-known for sex reassignment surgery. Public hospitals in Bangkok are usually of an acceptable standard and have English-speaking doctors available, though they tend to be understaffed and overcrowded and consequently, waiting times are long. However, the quality of healthcare and availability of English-speaking medical staff can fall sharply once you leave Bangkok and head into the smaller cities and rural areas. The top private hospitals, on the other hand, are among the best in the world, and while vastly more expensive than public hospitals, are still very much affordable by Western standards.
Most major cities in Thailand have at least one private hospital that is used by Western expatriates, and while they are more expensive than public hospitals, they provide a higher standard of care with English-speaking doctors and nurses, and are still reasonably priced by Western standards. Bumrungrad International Hospital in Bangkok is a world-renowned hospital for various surgical procedures that attracts medical tourists from far and wide, while the Bangkok Hospital group is Thailand's largest private healthcare group, and operates hospitals in many of Thailand's major cities.