What can cause a smelly vagina after sex?

How should a vagina smell?

Your vagina is a carefully balanced ecosystem and will usually be a host to a community of good bacteria. The main bacteria is called Lactobacillus, similar to the type found in live yoghurts.

Lactobacillus generates lactic acid and hydrogen peroxide which keeps vaginal pH at the ideal range of 3.5-4.5. These acidic conditions act as a disinfectant and discourage unwelcome bacteria from causing infections. It is these natural bacteria that can contribute to a vagina's natural scent.

Vaginal odour and sex

Like the armpits, the groin has a high concentration of sweat glands. During exercise and sexual activity, it is normal for the genitals to get sweaty and this may contribute to a stronger vaginal odour.

However, if you notice a stronger fishy smelling odour after sex, it could be an infection called bacterial vaginosis (BV). BV occurs when the balance in the vaginal ecosystem is disturbed, allowing a bacterium called Gardnerella vaginosis to thrive. The infection causes thin, grey, fishy smelling vaginal discharge that is more pungent when in contact with semen. Your GP can help diagnose this and administer treatment.

Can semen cause vaginal odour after sex?

Semen is normally a white or grey coloured fluid that carries the sperm and has a mild chlorine-like smell. With sexually transmitted infections (STIs), it is possible for the semen to change colour to yellow or green and smell unpleasant. This means semen could be the cause of vaginal odour after sex.

After ejaculation into the vagina, most semen will either seep out or dry up. The vagina is a self-cleaning organ, and any remaining semen will exit the body via a woman's discharge. Sperm can survive for a maximum of five days inside the vagina.

Other reasons for vaginal odour

Other things may affect vaginal smell, without meaning that there is something wrong with your hygiene or vaginal health. These sources of vaginal odours include:

Hormonal changes

Vaginal odour may vary in response to your menstrual cycle, pregnancy and menopause.

Medication

Hormonal treatment such as the contraceptive pill and antihistamines can dry the vagina out and change its odour.

Diet

There is no scientific proof that diet affects vaginal odour, but anecdotal evidence has suggested the smell of your vagina may change with certain foods, such as garlic, onions and strong spices.

Potential causes include:

• Poor hygiene.

• Sexually transmitted infections- such as trichomoniasis.

• A forgotten tampon.

• Thrush infection.

• Rectovaginal fistula - an abnormal connection between the vagina and the rectum, most commonly due to bowel problems like inflammatory bowel disease, childbirth-related injuries, cancer or cancer treatments such as radiotherapy.

• Vaginal and cervical cancer.

The dangers of over-cleaning

You may see lots of feminine hygiene adverts encouraging you to keep your vagina clean and smelling sweet - ignore these

Your vagina is self-cleaning. Using feminine hygiene products can affect your natural microbiome, leaving you more vulnerable to vaginal infections - and accompanying bad odours.

One study demonstrated that women using feminine hygiene products or douches were more likely to have bacterial vaginosis, yeast infections, sexually transmitted infections, and urinary tract infections (UTIs).

Avoid harmful products and simply stick to the following advice to keep your vagina healthy:

• Wipe front to back when going to the loo.

• Wash your external vaginal area with warm water or a mild soap when in the shower.

• Avoid harsh or irritant soaps.

• Don't douche.

• Wear loose-fitting, breathable cotton underwear.

• When menstruating, change tampons and sanitary pads every few hours or when your pads get wet or uncomfortable.