Turmeric is an amazing substance. It is used medicinally to prevent and treat a variety of health issues. Unless you use it in massive quantities there aren't any real side effects.
Of course, if you are allergic to turmeric you shouldn't use it topically or ingest it. If you've never used it before, it's a good idea to rub a small amount on your skin and look for a rash before you consume turmeric orally. Due to its ability reduce the clotting of blood, if you're being treated with medications for high blood pressure or with other blood-thinning drugs, you should avoid using turmeric. And like any other medicine or herb, there can be interactions between drugs so check with your doctor or pharmacist if you are taking other substances.
The Federal Drug Administration (FDA) has not yet issued any recommendation regarding turmeric. However, a similar governing body in Germany has declared turmeric hazardous only to those suffering from biliary obstruction. It has also cautioned those with ulcers or gallstones or other gastrointestinal ailments to avoid turmeric.
Studies have concluded that ingesting vast amounts of turmeric is harmful to red and white blood cells. However, the amount of turmeric involved is enormous to cause this type of damage. It also should be noted that the effects of turmeric on pregnant and nursing women are unknown.