What's the difference between STIs and STDs?

STDs stands for “sexually transmitted diseases,” while STIs stand for “sexually transmitted infections”. They are often used interchangeably. “Disease” suggests a medical problem associated with clear signs and symptoms. Since several of the most common sexually transmitted bacteria and viruses have no signs or symptoms, it is more accurate to refer to them as infections rather than diseases. Also, the use of STI instead of STD reflects the reality that not all sexually transmitted infections turn into a disease.