Sexual desire is often confused with both libido and arousal. These three terms are usually spoken about and used interchangeably but are rarely fully understood.
Libido is commonly used to describe sex drive, but its usually seen to be binary - so its either high or low. Arousal is the collective term for the physical changes that enable the body to be ready for sex - such as raised heart and breathing rate, and increased blood flow to the genitals.
But in medical terms, desire is a person's want to have sex, which is a fluid situation.
Like many human behaviours, sex is a habit. Yet there is no normal frequency of sex and amount of sex thats good or bad. Instead, frequency, duration and type of sex is down to what each individual finds pleasurable.
People want and have sex for many different reasons. Classically, sexual desire was thought to be a sex drive, with people having either a low or high drive. It was presumed that this was fixed and an inherent part of all of us. But this led to many women being mislabelled as having low sexual desire, simply because they didn't want as much sex as their partner.
This theory was overtaken by the dual control model of sexual response. This states that there are two independent processes going on that feed into our sexual response. One is excitatory and activating, whilst the other is inhibitory and deactivating.
The balance between these two opposing processes determines our overall response in any given moment. This is like a car with an accelerator (excitatory) and brake (inhibitory).
How much accelerator and brake are applied when it comes to sex will vary between people and also fluctuate within a person. People may have more accelerator or brake overall, but each situation will be different. So, desire is complex, individual and dynamic.
A more in-depth look at the science of sexual desire reveals we can split it into two different types - spontaneous desire and responsive desire. Spontaneous desire shows up instantly and can occur with or without stimulation. Its typically high when people are young and/or at the beginning of anything new a relationship or situation.
In contrast, responsive desire is a reaction to an external stimulus such as a book you're reading, or having dinner with your partner and tends to be greater in longer term relationships, where spontaneous desire may have reduced.
These two types of desire are built into an alternative model that critically addresses women's sexual response. It acknowledges the two types of desire and explains that they may come before or after arousal. In this way it better reflects how women feel about, respond to and experience sex.
It also incorporates the key role of intimacy being physically and/or emotionally close - and acknowledges how that's often a strong factor in motivating women to want to have sex.
Of course, there are also many biological, psychological and social factors that can affect sexual desire.
If you are suffering from a physical condition, such as aching joints, vulvodynia (a condition that causes pain, burning or discomfort in the vulva) or genitourinary symptoms of menopause, which causes sex to be painful, you'll be instantly put off.
This will follow through to the next experience, and put you off even more. In this way, your inhibitory processes will dominate your excitatory processes, and damp down your desire to have sex.
We naturally don't want to do things we don't enjoy and this also applies to psychological issues as well as physical ones. If we don't feel comfortable, for example, due to our body image, or we are in a strained relationship, we wont enjoy sexual experiences and this will affect our view of sex overall and our ability to feel sexual desire.
Also, there are external distractions that can inhibit desire. The routine of normal life work needing to be done, food needing to be made, children needing to be looked after etc, simply gets in the way. A never-ending to-do list and constant tending to others' needs can quietly and consistently affect your body and mind's ability to produce responsive desire, let alone provide space for spontaneous desire to be felt.
Great, pleasurable and fulfilling sex is a behaviour that's cultivated, rather than being ever present and automatic. It is not as simple and set as you have it or you don't, but more a fluctuating situation which needs to grow and be nurtured. But this is not fully understood by most people, which leaves them confused about their own attitude to sex and can lead to problems.
It doesn't have to be this way. Better education on the science of desire would give insight into our own sexual motivations and lead to happier and more fulfilling sex lives.