Have you ever felt like your body odour changes from one day to the next?
It can be a little gross, but sweating is completely normal, as is a little variation from time to time in the quantity and scent.
Here's what experts have to say about the relationship between body odour, sweat glands and hormones.
Different types of sweat
Deshan Sebaratnam, a dermatologist and associate professor with the University of New South Wales, says there are "different types" of sweat glands.
Eccrine sweat glands are distributed over the entire body, for example, on the forehead, where Dr Sebaratnam says sweat is less likely to encounter the bacteria that makes it smelly.
However, apocrine sweat glands are found in places such as our armpits and groin, where there are hair follicles.
"They don't just release water and salts and things like that, they also release other chemicals, [and] these chemicals then get broken down by bacteria," Dr Sebaratnam says.
Those bacteria dying contributes to bromhidrosis, a medical term for excessive or unpleasant body odour.
Dr Sebaratnam says where the sweat is coming from can make a difference.
"There are other variations like how much you're sweating, how easily it's wicked away, the environment, and maybe your own perception or awareness."
What role can hormones play?
Pav Nanayakkara, a gynaecologist at Jean Hailes for Women's Health, says hormones help to regulate lots of different bodily functions.
"One of them is temperature and there can be lots of different hormones that help regulate this," she says.
"During various phases of a woman's reproductive life … there's big shifts in hormones, but even within the [menstrual] cycle itself there can be some shifts."
For example, after ovulation a woman's oestrogen levels start to fall and progesterone levels can increase. Dr Nanayakkara says patients can feel hotter and produce more sweat as a result.
Dr Nanayakkara also says falling oestrogen levels and higher amounts of androgens such as progesterone and testosterone, which occurs after ovulation and also around menopause, can "change the composition of sweat, but also make it more appealing to bacteria".
This can mean your body is producing "certain thicker compositions of sweat that bacteria like more, and then you get more odour associated with that".
"All of the odour that comes from sweat is from bacteria," Dr Nanayakkara says.
What's an ordinary amount of sweat variation?
"Some people don't sweat at all, other people sweat a lot," Dr Sebaratnam says.
He says hyperhidrosis is a condition that may apply to those of us who sweat excessively. The condition can impact particular parts of the body, such as the face and head.
In some instances, a change in the amount or odour of sweat could indicate a more serious condition, Dr Sebaratnam says.
"If all of a sudden you notice a change in the quality of your sweating, then that's something that should prompt you to see a doctor [or dermatologist about]."
Dr Nanayakkara says fluctuations, such as those through a monthly menstrual cycle, are normal.
But she says if sweat "suddenly starts to become persistently odorous, one of the things [for women] to be thinking about is, you know, are my oestrogen levels falling is, could this be a sign of menopause?
"Obviously it depends on what age the patient is, but you might be starting to look for other symptoms.
"Any change that's persistent may warrant further investigation."
How to manage smelly sweat
If you want to manage your body odour, Dr Nanayakkara suggests starting with non-invasive methods such as deodorant and tweaking your diet and exercise routine.
"We know that things like spicy foods and red meats can increase body odour, whereas things like fruit and vegetables tend to reduce odour."
She adds that exercise may also "help balance hormones".
For managing the odour itself, she recommends "gentle soaps and cleansers for higher-risk areas like armpits and groin areas."
Dr Sebaratnam says "over-the-counter, aluminium-based antiperspirants" can help. He recommends applying it at night, after a shower when you're relaxed and not sweating.
Deodorant that can help "mask" body odour and over-the-counter skin products with benzoyl peroxide can help clear the "bacterial load" that causes sweat to smell.
There are also treatment options, such as medications and Botox, for those who experience excessive sweating, he says.
But, for most of us, sweating is completely normal, even if it occasionally makes us a little more smelly.
This is general information only. For personal advice, you should see a qualified medical practitioner.
