Shoulder and hand bags produce postural deviations in all planes, which can lead to negative stresses and strains on the spinal structures and ultimately to pain and progressive postural scoliosis.
Carrying a handbag or any other type of bag over the shoulder is an extremely common habit that can lead to postural distortion. Although the weight of the bag is important, as it weighs on the shoulder girdle muscles through the strap, this weight is not the most important aspect. Even carrying an empty rucksack creates a postural distortion due to the contraction of the muscles that raise the shoulder girdle. The reason for this is that the natural slope of the shoulder is such that a bag would fall.
To prevent this from happening, the person isometrically contracts the musculature to elevate the scapula to avoid this. This long-term isometric contraction eventually leads to a chronic postural problem, regardless of the weight of the bag (although heavier weights force the muscles to contract with more force). Wearing a pack with the strap across the body over the opposite shoulder is healthier, as it eliminates the need to isometrically contract the muscles to change the shoulder angle.
