Nitric oxide (NO) improves the blood flow to various parts of the body by dilating the veins. Sexual stimulation promotes the production of NO in the penis and dilates the veins, ready for the increased blood flow to enable a strong erection.

In the same way, in women, the veins in the genital area are dilated which improves sensitivity and sexual response.

There are various reasons why NO levels might be low. How Does No Work For Sexuality ?