This is fast becoming a major problem in modern dentistry. Enamel which covers your teeth is very strong but excessive acids in your mouth will dissolve enamel away.
If you also rub at your teeth when acids are present this will speed up the wear. This can be either excessive brushing or scrubbing with a tooth brush or clenching and grinding.
Acid can come from outside your bodies from food and drinks or inside from medical conditions.
Common drinks like fruit juice and smoothies, fizzy pops and herbal teas together with citrus fruits and pickles can all increase the wear of your teeth.
Indigestion can be a sign of medical conditions were stomach acid regurgitates into your mouth. You should speak to your doctor if this is a concern.
Some people have low quality saliva which does not fully protect your teeth, this can be caused simply by being dehydrated as well as some medications. Tooth mousse is an excellent product to help protect your teeth from acid erosion.