Travelers have little to worry about in a country where the health standards are ranked among the highest in Asia. For tips on avoiding some of the most common diseases in Malaysia, you can read about this post, Avoid Falling Sick When Travel in Malaysia.
Water in cities is generally safe for drinking, but it is safest to drink it boiled. Bottled drinks are also widely available. Avoid drinking iced water from roadside stalls. It is important to drink sufficiently to avoid dehydration. Drink more than you would normally if you are from temperate country. Cooked stall and restaurant food is generally safe to eat.
The sun is strong in Malaysia. One hour of sunbathing a day for the first few days will get you a lasting tan without giving you sunstroke.
If you are visiting remote rainforest areas, it is advisable to take protection against malaria. See your doctor before leaving home. Malaria tablets are only available on prescription in Malaysia. To keep mosquitoes at bay, use insect repellents, mosquito coils and mosquito nets at night.
Treat open cuts and scratches immediately as infection in humid climates can delay healing and at worst cause tropical ulcers. It is advisable to read up about which rainforest and marine creatures to be wary of.
Medical supplies and treatment are readily available in Malaysia, in pharmacies and hospitals as well as at 24-hour private clinics.