The main problem, afflicting women much more than men, is that of orgasm failure. While a few women seem capable of orgasm by fantasy alone, most require manual or oral stimulation in addition to intercourse, and some never achieve orgasm at all. The flip side of female orgasm difficulty is premature ejaculation, though it is not always clear whose problem this is. If a man ejaculates before getting his trousers off it is fair to say it is his problem. At the other extreme is the definition that a man is a premature ejaculator if he reaches orgasm before his partner on more than half of all occasions of intercourse regardless of how many hours he may perform. Some intermediate definition is more helpful.
In men arousal problems are either caused by a variety of psychological factors: stress, fear of failure, disease or punishment. Physical factors play an important part. Alcohol is also widely recognized as a cause of impotence. Age and fatigue may be implicated, and so may certain diseases such as multiple sclerosis, diabetes, tumours and hormonal disturbances. Increasingly it is being recognized that some medications, especially drugs used to reduce blood pressure may cause potency problems as a side-effect. Arousal disorder in women is less public. Sometimes it is a straight forward lack of lubrication.
Disorders of appetite are increasingly recognized as important, particularly in women. A high proportion of women complain that they are just not sufficiently interested in sex to keep their partners happy. In some periods of history this would have been considered normal. Today with the powerful myth of male/female identity, women who have little interest in sex are made to wonder what is wrong with them. If men had the same interest in sex there would be no problem. Because the libido cannot easily be reduced by other than chemical or surgical means and an interest in sex can be increased by use of erotica, fantasy, foreplay, role playing, [etc], the partner with the lower level of sexual appetite is more often seen as the one to be treated. Another disorder of appetite that effects men more often than women is the resistance that arises from repeated sex with the same partner. A tendency for males to be sexually recharged by novel females is observed in most mammals. This may manifest itself as a specific loss of appetite for the wife, even though the man may love her in other ways.
The final category, concerned with orientation or target of sexual interest is more relevant to men than women. Homosexual orientation, as opposed to occasional homosexual behaviour, occurs in something like 5% of men and 1% of women. Sexual deviations such as fetishism, transvestism, sado-masochism, paedophilia, zoophilia and other unusual preferences are almost exclusively male.