2. Thymus droop will not only cause some erosion or eczema of the skin, which is caused by friction or high temperature at the folds of the two breasts. The main problem leading to breast ptosis is skin relaxation. Breast ptosis is a physiological phenomenon, which is common in women in the third trimester of pregnancy or after lactation. This is because the proliferation of breast and connective tissue in female breast leads to the enlargement of breast, but the elasticity of stretched skin and suspension support structure decreases when the breast is enlarged, which leads to the sagging of breast and looks like a bag.