First, I need to make a couple of general points about labelling what people do when they overuse or over-do anything as an “addiction”. The same goes for labelling the person as an "addict" This is too easy a way out. What we should be doing is describing the person more accurately as someone who:
1. Is suffering from deep emotional pain, or emotional wounding usually carried from childhood. What they are doing in the short term is medicating, usually over-medicating, their emotional pain, as I explain below. There are some who claim that addictions are inherited and that is true in a small number of cases. But I have never yet met a person in an addictive cycle who deep inside wasn't greatly troubled by emotional pain or emotional wounding. What is described as their addiction is whatever they find helps medicate their wound or reduce their pain.
Your notice that when I write about addictions I use the term "medicating" a lot, mainly because this describes what is happening inside that person far more accurately and secondly because that gets away from some of the shame that they feel whenever they are labelled as a person suffering from a bad disease, a bad habit or lack of willpower. It is no coincidence that usually the deep emotional pain or wounding as a very strong shame element within it, so shaming makes the pain worse.
2. Is in denial. Which is a rather judgemental way of saying that while they are under the influence of their particular medication (their addiction) and, or while they are suffering from deep emotional pain, it is impossible for them to see clearly what others can see  them doing. Usually they are in one or the other state, which is why it's often said that all addictions involve denial.
3. Is trapped in "an addictive cycle" because this is really what is happening inside them.
I have written about this on a separate page and described the various stages in the cycle which people we like to call "addicts" are really going through as they get trapped further and further into their addictive cycle.  Go to Overview of Addictive Substances and Activities
As I explain on a separate page someone trapped in an addictive cycle is not a "bad" person, even if the things they do are very wrong.  They are not giving in to a "bad habit" which they could easily overcome with a little willpower.  Even if they could stop medicating they would still have the emotional pain and in many cases that is unbearable.  Go to Overview of Addictive Substances and Activities
I also have a personal rule that no one has the right to label anyone else an "addict" unless they acknowledge that they too are one and therefore have some real understanding of what is going on, so at that point I need to go on record here and acknowledge that I too am a recovering addict, from not one but several different forms of medication. I too spent many years trapped in my own addictive cycles. It and it took some amazing people in a number of different Twelve step groups, and some absolutely wonderful addiction counsellors to teach me how to get out of the trap and free myself from the cycle.  By the way, as any recovering addict will explain to you I may be in recovery but I will never be free of the addictions themselves. The day I believe that I am free of them is the day they will return.

What is "medicating" in this particular case?

1. Using external substances like alcohol, nicotine, sugar or illegal substances which in turn produce brain chemicals which relieve the emotional pain. Go to Overview of Addictive Substances and Activities
2. Medicating on internal substances.  These are brain chemicals and hormones produced by the body as a result of physical activities, for example gambling, excessive exercise, work-holism, anorexia, bulimia, co-dependency and unbalanced sexual activities. In each case the person has found that for them one specific kind of activity encourages their body to produce special, make that very special chemicals which help reduce their emotional pain. It's important to note that these do-it-yourself body chemicals relieve emotional pain far better than any external substance. They are also highly addictive. Go to Overview of Addictive Substances and Activities
To keep things simple in this article when I use the short term "sex addiction” now you know what I mean. I acknowledge that this article is only about identifying sex addiction and offers no solutions. On other pages I do offer some standard "do’s" and "don'ts" but in the case of sex addiction there is absolutely no way that this can be resolved by reading articles on the website or in a book. This is one of the ones that requires either professional help or regular attendance at a Twelve Step group (for example Co-dependents Anonymous CODA  or Sex and Love Addicts Anonymous SLA) preferably in conjunction with one-to-one professional help.
However, it is seldom that an addict ever seeks professional help or joins a Twelve Step group until they have first accepted the reality that they are stuck in an addictive cycle. This page is to help create that reality and help break through denial (Go to the bottom of the page Overview of Addictive Substances and Activities

Signposts that point toward a sex addiction cycle
Signs in this case like signposts. By themselves pointers do not constitute proof, but the more signposts there are the more likely that what they are pointing towards is the presence of some level of sex addiction. If you are considering whether someone you know is in a sex addiction cycle keep in mind that they are not likely to come out and make you aware of these signposts. On the other hand if you think that you might in the cycle yourself you may find these pointers are a help.
Medicating on sex is often first observed  by the person’s obsession with talking about sex, seeing and hearing sexual innuendoes in even the most ordinary situations and conversations.  There may also be a number of behaviours which might or might not be noticed by other people.

These can include any of the following:

v inability to achieve true adult intimacy with only one person.
v having multiple sex partners or regular one night sexual encounters without commitment
v regularly changing sexual partners or dating a series of different but ‘regular’ or serial sexual partners within the same period
v  if in a long term relationship, having regular affairs outside that relationship and letting the partner know about these
v  regular use of phone sex or sexual interactions using the Internet’ or E-mail to allow sexual gratification without closeness or commitment
v   compulsive and excessive masturbation if used as a means of avoiding physical intimacy with a partner
v   compulsive or obsessive use of pornography especially if used as a means of avoiding physical intimacy with a partner
v regularly visiting massage parlours, strip shows or other sex services while avoiding close relationships
v  spending large sums of money on sexually explicit videos, magazines or sexual subscription services on the internet. Keeping a large supply of such material on hand as a ‘stash’
v   making unwelcome or inappropriate sexual advances or sexually harassing other people
v  making indecent phone calls, voyeurism, exhibitionism or ‘flashing’
vforcing any person to take part in unwanted sexual activities, including sexual abuse, forced sex, incest, or child molestation
v  an obsessive desire to take part in unusual or bizarre sexual practices

What about “kinky” stuff?
Keep in mind that it is normal for couples in a mature intimate relationship to experiment with a range of novel or offbeat sexual practices, for example viewing pornographic videos or discussing the possibility of experimenting with unusual sexual activities (many of which they may never actually get round to trying). However these are not necessarily signs of sex addiction as long as they take place in private and provided both parties not only consent but find the activity provides some enjoyable sexual stimulation. The more random or occasional the offbeat activity, the less the chance it is related to sex addiction.  Even if both partners are comfortable, the more regular and repetitive the pattern the greater the possibility that some element of sex addiction is tied in with the activity. The less one partner is participating with enthusiasm the more the likelihood of sex addiction in the other partner.
It is also normal for couples to share sexual fantasies that involve strange or unusual activities which neither would dream of acting out in real life. Again, the less enthusiastic one partner is about this the more there may be a pointer towards sex addiction in the other partner.
However, if one partner wants to start acting out these fantasies in real life and especially if this would require a break in intimacy or commitment it is almost certainly a pointer to a growing level of sexual addiction.

Endorphin
Another common signpost is a reduction in emotional pain which results when the sexual activity produces a rush of a natural brain chemical very similar to morphine. Endorphin is a powerful pain reducer but the effect in this case  is unfortunately much like their effect on a gambler following a winning streak. Like a gambler, he or she goes into denial, fails to see that he or she is doing terrible damage to their body or their life and feels no fear, pain, guilt or shame about what they are doing. And because endorphins are chemically very similar to morphine at the same time as they are reducing feelings of emotional pain they are also seriously raising the level of addiction.
A second body chemical, adrenalin can also be involved.  A person who, after sharing orgasms with another person, often gets angry, shuts down emotionally or isolates from their partner may be using endorphin or adrenaline or both as a medication. This is in contrast with what the partner expected in terms of enjoying mutual closeness and affection. The medicator is actually experiencing withdrawal symptoms because after orgasm their adrenaline and endorphin flow is reduced.
Sexual Anorexia
Sexual anorexia is also a form of sex addiction. The sexual anorexic obsesses about avoiding anything sexual. The high they get from this avoidance is similar to the  adrenalin-based high experienced by an anorexic who avoids eating as a way of medicating or lessening their emotional pain. As with eating disorders the sexual anorexic usually has occasional bouts of "sexual bulimia", that is excessive sexual activity followed by "purging".

Hidden  pointers

One of the most significant but well hidden signs that a person is medicating on sex is their strong attraction to (and usually their active involvement in) sexual activities which are unusual, risky, more often both. However this sign  is usually not going to become obvious to anyone else until quite late in the cycle.
The excitement is generated a psychological high caused by a rush of adrenaline.  That suggests the probability that the resulting "high" is not the same as the normal excitement from sexual stimulation or orgasm.
A  second hidden pointer is a history of untreated sexual abuse as a child or teenager, which will be closely related to the deep emotional pain or wounding or shame which they are medicating but of course many individuals will do their best to avoid revealing this history.

See also 

Addictive cycles - over medication and vulnerability