In general terms, asexuality refers to people who don’t feel driven to have sex. They do not necessarily have negative feelings about sex. They just don’t feel sexual attraction to others.
However, asexuality is not quite that simple. Some experts describe asexuality as a continuum. For example, many asexuals enjoy committed relationships and develop strong romantic feelings for their partners. However, those feelings are not sexual ones.
Some asexuals do have sex in order to please partners who have sexual feelings. Often, sex is a negotiated aspect of a relationship.
Other asexuals feel sexual once they have been committed to a partner for a long time. Some may have sexual feelings on occasion or masturbate as a form of pleasurable relief. Others never feel sexual urges.
One important distinction about asexuality is the lack of distress. Usually, asexuals do not feel bothered by their feelings about sex. Asexuality is just part of who they are.
In contrast, some people feel greatly distressed by diminished sexual desire. In these cases, treatment may be considered. Low libido can be caused by many factors, including hormonal changes during menopause, low testosterone in men, and health conditions like diabetes. It can also be a side effect of medications.
Sometimes, low sex drive is situational. For example, new parents are often too exhausted to want sex. Or, partners experiencing stress in their relationships may not feel inclined toward intimacy.
There are also times when women lose their desire for sex with no clear-cut explanation. This is called hypoactive sexual desire disorder (HSDD). (See common questions and answers about HSDD here.)
People who feel distress due to low libido are encouraged to see their doctor, who can assess the possible causes. Sometimes, a change in medications or a course of sex therapy or couples counseling will help.
But those who do not feel distress over a lack of sex drive probably don’t need to worry.