Having your straps come off your shoulders, is very irritating. This guide is about keeping bra straps from slipping.
Read and rate the best solutions below by giving them a "thumbs up".
Try nipple pasties on your shoulders to stop a loose bra strap from slipping They are flesh coloured with a thin gel to give comfort and grip. They are cheap, reusable and self-adhesive. I just thought of this! It works as far as walking around the house though I have yet to test this going out. I hope this helps.
To keep your bra straps from slipping off of your shoulders cut a 2 inch rectangular piece of rubberized shelf and drawer liner and place it on your shoulder under your bra strap. It works!
By Lois 
Use a Band-Aid to hold your slipping bra strap in place. Simply place the
Band-Aid over the strap across your shoulder and your strap will
stay in place all day without you constantly having to pull it back up.
By Linda 
To keep bra straps hidden, I have recommended the double stick tape (sometimes called "fashion tape" or such) between the dress and bra strap. You can even add a piece again between the skin and the strap-package.
A better idea, that is more re-useable, would be to sew in the oval spring clip type hair clips (child sizes) with a loose tack (so it moves a bit). Can be fastened with one hand and is always ready in the dress/shirt.
Source: Clips were my brainstorm after those little snap-things drove me crazy.
By OrahLee from Tucson, AZ
Have you seen the mini-infomercials for the round plastic bra strap holders to allow you to convert your bra for inward-facing t-shirt straps - so that your bra doesn't show? I hate that.
Well, in the ad, they show a close-up of the actual item. I'll be darned if I'll pay $20 for 6 of these things. So I just took the clear plastic lid off a can of finished peanuts, made my own circle, used a craft knife to cut the inner grooves and I now have a fancy strap converter. Sure, I smell a bit like nuts - but since I'm nuts it all goes together.
Source: The infomercial for the plastic bra-strap converters
By Barbara from Wickliffe, OH
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Here are questions related to Keeping Bra Straps from Slipping.
How can I keep my bra straps in place? I wear a Genie bra, and the straps are different than the usual bra.
By boocat 12/11/2014
I hand sew a strip of soft elastic, 1/4 inch wide from one side of strap to the other, not tight, probably midway between top and hooks. You have to step into bra, but I'll take that over straps falling off.
How do I keep bra straps from sliding off my shoulders?
By Sharon from AL
By Elaine 03/19/2010
Some bras have little rings on them where the bra strap is attached. I take a piece of elastic and sew it to one ring and then to the other (across the back), making it small enough in length to pull the straps slightly to the center. I had bought some of those from Bali too but they are expensive for what you get. So when I make them, I just go by the ones I got from Bali to make the correct length. I can't give you a correct length here because we all have different sizes. I hope I made it clear. If not send me a message and I will try and clarify.
By Ginny 03/17/2010
I had the same problem; it's from having shoulders that slope downward instead of out. Bali makes a great set of silicone wing shaped thingies that you slip your strap into and they stay in place. They are about 6 or 7 dollars a set and worth every cent.
The other thing to look for when you get a new bra is to see if, on the back, the straps are more toward the center and not the ends. It doesn't have to be like a sports bra, just a little more toward the center-it makes a huge difference. Now that I know that, I only have to use my silicone things on old bras that have straps more toward the outside. Hope that helps!