Is there a type of vaginitis that is an STD?
Trichomoniasis is a type of vaginitis that is sexually transmitted, and other STDs (gonorrhea, chlamydia) can cause vaginitis-type symptoms as well, so it’s important to be tested if you are at risk of having been exposed to an STD. The vaginal discharge associated with gonorrhea and chlamydia is sometimes more discolored (green-yellow) than BV or yeast, but differentiation cannot be determined by color alone. If at risk, testing is critical.
Beyond that, neither candidal vulvovaginitis (yeast infections) nor bacterial vaginosis (BV) are sexually transmitted diseases, but anything inserted vaginally (whether a body part or sex toy) can disrupt the bacterial balance of the vagina and potentially cause BV. Some women are more sensitive to bacterial imbalances than others, making them more vulnerable to developing BV as a result of penetrative sex. It’s also worth noting that the fishy odor of BV is often more pronounced after contact with semen due to the high alkalinity of both BV and seminal fluid, but this does not indicate a change in the severity of the infection.
BV can also increase the risk of contracting other STDs. We don't know exactly what the mechanism is behind the increased risk, but it may have to do with the disruption of pH balance or the general vulnerability of the vaginal tissue. For that reason, if you have BV and you don’t know don't know the STI status of your partner, be sure to use condoms.
As for yeast infections, sexual partners do not generally transmit fungal infections to one another during sex, so these can’t increase the risk of contracting other STDs. Yeast infections often develop after prolonged periods of exposure to moisture (think swimsuits, or sweaty gym clothes) but not necessarily in connection with sex.
While not an STD, “cyclic vaginitis” is sometimes used to describe symptoms of BV or yeast occurring in cadence with the menstrual cycle. For some people, having a period resets the pH balance of the vagina so that if you do have symptoms of vaginitis just before your period, the period itself will clear things up. But for others, the change in pH that is a byproduct of bleeding can trigger BV or a yeast infection, resulting in cyclic vaginitis. Cyclic vaginitis can be approached like other types of recurrent vaginitis. Rather than treating this as a set of independent, monthly episodes of infection, a long-term treatment approach is generally more effective.