Bra Straps

I've got that problem.....always the left side, because I am lopsided due to scoliosis.

I think there are several types of rubber non-slip cushion things for bras on E-bay and Amazon which prevent this kind of slipping.
Should solve the problem and be more comfortable for you.

Perhaps you can get a fitting. If the strap is not on your shoulder there is no support, which you really need with 40G. I read somewhere once that if the breasts are not supported the tissue will stretch and sagging will not be revertible.

Tighten the elastic in your straps, use the non-slip pads, get a fitted bra and don't wash it too hot or too often. Replace the bra as soon as it starts to get loose. Try some exercises to improve your posture.

I was always hitching up my bra and getting wet patches on my clothes from doing it as it mainly happens when you're doing the housework, especially cleaning floors. Recently I ordered a new bra in one more desperate attempt for comfort and stay-up-ability and I finally found one. I slipped it on to try when it arrived and was so delighted I kept it on without even washing it first! I immediately ordered 2 more.

Usually people go for too large a measurement and too small a cup size but it sounds like with 40G you have got the balance right. However, a fitting and investing in one expensive bra might be worth it.

You could put a velcro strip on your top so that when the bra is on, it's folded over and sticks to itself so keeps bra in place.
Or something like this

amazon.co.uk/401170-Shoulder-strap-retainers-pieces/dp/B00426OKY0/ref=pd_sbs_201_4/259-2724472-1893315?_encoding=UTF8&pd_rd_i=B00426OKY0&pd_rd_r=1b7a0ec9-61f0-11e9-95c1-6d8c73d1e722&pd_rd_w=9twjQ&pd_rd_wg=cWLzj&pf_rd_p=18edf98b-139a-41ee-bb40-d725dd59d1d3&pf_rd_r=AS97EAKYF3QCEC18PHXE&psc=1&refRID=AS97EAKYF3QCEC18PHXE]]

I have the same problem on my left side. It has only started the last few years.
You can get some silicone shoulder strap protectors from eBay that are very cheap and do solve the problem (if you remember to use them). They are very easy to use too.

I am also careful to choose a style where the straps are set from the centre of the cup and sit on the centre of the shoulder. Some bras have straps set to the sides.

I have a problem with the left side and that is because, I think, I always carried my satchel on my left side and then my handbag on that side.
Now I tend to wear a crossbag

However, the problem still persists!

This happened with me too! Always the right one then I figured the main problem is fitting only. As we grow old the size becomes smaller somehow, so the proper type and shape of bra is very necessary. I now use tight cotton fitted strap with all the adjustments

Yep, me too. My right shoulder.
I have a thin elastic which attaches to the straps and goes across my chest and ever-so-slightly pulls so they don't fall off my shoulder. Fine on higher necked garments such as t-shirt but useless on anything more revealing.

I guess if you have a partner, you could attach it across your back?

I should really be efficient and make proper, buttoned loops but I'm afraid I just use safety pins.

Incidentally, how amazing and possibly scarily intrusive is technology these days. On the side bar of this post, adverts for bras came up.

Scary intrusive algorithms!
I have narrow shoulders too and have trouble carrying a rucksack. I've tried tying the straps with a bungee.
For bras I always get properly fitted as my shape changes.
I would avoid housework!

Another one with narrow shoulders here !

I simply can’t get a bra to stay on my shoulders no matter how I tighten the straps, they just work their way down and slip off anyway. I am wearing a 36D but a recent visit to Marks said I should be wearing a 34 D but it feels far too tight and makes my back fat stick out, which is never a good look .

I have this problem too, I feel that narrow (and round) shoulders don't help. Tightening them up helps but needs to be done on a regular basis - almost every day. There's a happy medium isn't there - somewhere?
I wrote to M&S to complain about them and to suggest that the straps should be placed nearer to the centre back to help combat this. I got a positive response.
Also, I suggested that the buckles (or whatever they're called) should be at the front to make easy adjustment so that you don't have to twizzle it round three times or more to get it right. No wonder it takes so long to get dressed each morning.

Marks and Spencer do a bra that has silicone incorporated in the straps it stops the slipping and I had several but then I started to wear sports bras which seem to solve the problem too, not pretty but as it’s only me that sees them I’m not bothered. My slippage is always the right side never the left I’ve never figured out why that is.

It has just occurred to me (my brain!) - have you tried 'strap-traps'? If you google it there's a video on You Tube with a young lady demonstrating how to make your own.
They're a strap with a press stud attached. You can buy them in John Lewis with safety pins attached. I've sewn them into the shoulders of my summer dresses which seems to help.
It's worth giving them a try.

Me too. I'm another lop-sided one and always have problems with bra straps. I'll try some of the ideas above.