There are a lot of misconceptions around what sexual desire is, what is should look like, what is normal and abnormal. Some brief psychosexual education is needed here.
First and foremost, we need to get to know the concept of the sexual response cycle. This is the description of the physiology of human sexual response. And it begins with desire. Desire means 'interest in' or 'appetite for sex', like hunger and thirst. After desire, comes the physiological arousal stages of excitement and plateau, and the final stage of orgasm followed by resolution.
Low desire and desire discrepancy are the most common reasons people seek sex therapy, whilst others experience 'hypersexuality' where they feel out of control of their desire and behaviours.
How is it that some people struggle with lack of desire and others with too much of it? What controls when we're interested in sex? The best way to understand this is to get to know the Dual Control Model, which explains that central mechanisms govern your sexual arousal. To put it simply, the brain system coordinates sex through two mechanisms, a sexual accelerator (Sexual Excitation System (SE)) and sexual brakes (Sexual Inhibition System (SI)).
The SE system receives information about sex-related stimuli in the environment - things you see, hear, smell, touch, taste or imagine. Signals from the brain are sent to the genitals to tell them "Turn on!". It is always at work, far below the level of consciousness. You are unaware until you find yourself turned on and pursuing sexual pleasure.
The SI system is there to detect potential threats in the environment - again, things you see, hear, smell, touch, taste or imagine. Signals from the brain are sent to the genitals to tell them "Turn off!". This is like a foot brake in a car, looking for reasons not to be aroused - i.e. risk of STI transmission, unwanted pregnancy. This can also be fears related to performance, such as worrying about not having an orgasm. This also works all day, sending steady streams of messages to say "Turn off!".
So, when we apply this to understand sexual functioning and dysfunctions, we can see it as the balance between brakes and accelerator. If you have trouble with any phase of sexual responses, you might want to ask, might there be insufficient stimulation to the accelerator? Or is there too much stimulation to the brakes?
It is common for people struggling with desire or orgasm is to assume the problem is the lack of accelerator. Instead, the problem is most likely to be that there is too much stimulation on the brakes. I.e. what is hitting the brakes, and so often? Because, this then causes us from being unable to get aroused.
Individual sexual temperaments
We all have unique levels of how sensitive our brakes and accelerators are, which explain the different sexual temperaments or personalities. We may be high on both the brakes and accelerator, or low on both. We may be high on brakes and low on accelerator, or high on accelerator and low on brakes.
What do we do about it?
Well, we can't change the fact that we have mechanisms of brakes and accelerators, and how sensitive we may be to them. But, it is possible to change what the mechanism responds. For example, what do your brakes consider a potential threat to be? And then, you can reduce those threats, such as unwanted pregnancy or STIs or stress.
You could also change what the accelerator considers as sex-related, then increase sex-related things in your life. I.e. change the context, including external circumstances as well as your internal state.