Oral sex is good for women's health and makes you feel happier, according to a study which studied the effects of semen's 'mood-altering chemicals'.

The State University of New York study - which scientists carried out via survey rather than through practical experiment - compared the sex lives of 293 females to their mental health.

It follows research which shows that seminal fluid contains chemicals that elevate mood, increase affection, induce sleep and also contain at least three anti-depressants.

The researchers also claim that women who have regular unprotected sex are less depressed and perform better on cognitive tests.

Semen contains another of chemicals along with spermatozoa, including cortisol, which is known to increase affection, estrone, which elevates mood and oxytocin, which also elevates mood.

It also contains thyrotropin-releasing hormone (another antidepressant), melatonin (a sleep-inducing agent), and even serotonin (perhaps the best-known antidepressant neurotransmitter).

Given these ingredients - and this is just a small sample of the mind-altering 'drugs' found in human semen - Researchers Gallup and Burch, along with the psychologist Steven Platek, hypothesised that women having unprotected sex should be less depressed than suitable control participants.

To investigate whether semen has antidepressant effects, the authors rounded up 293 college females from the university's Albany campus, who agreed to fill out an anonymous questionnaire about various aspects of their sex lives.

Recent sexual activity without condoms was used as an indirect measure of seminal plasma circulating in the woman’s body.

Each participant also completed the Beck Depression Inventory, a commonly used clinical measure of depressive symptoms.

The most significant findings from this study, published in the Archives of Sexual Behavior, were that, even after adjusting for frequency of sexual intercourse, women who engaged in sex and 'never' used condoms showed significantly fewer depressive symptoms than did those who 'usually' or 'always' used condoms.

Importantly, these chronically condom-less, sexually active women also evidenced fewer depressive symptoms than did those who abstained from sex altogether.

By contrast, sexually active heterosexual women, including self-described 'promiscuous' women, who used condoms were just as depressed as those practicing total abstinence.

The research suggests it is not just that women who are having sex are simply happier, but that happiness levels might be related to the quantity of semen within their body