Why is wearing uniform a religious trouble in some areas?

For people with riligious belief, some people needs to wear head scarves or rings. For Muslims, it is important for them to wear head scarves because they need to hide their skin. For Hindu people, it is their own way to show the belief by wearing rings and many religious accessories. School uniforms sometimes hinder people from wearing bandanas and accessories, so those people, it is a big propblem that they cannot wear that they need to wear.