The formation of chest stretch marks is mainly related to skin damage and hormone level changes. 1. Skin damage: women during pregnancy fat, muscle and other subcutaneous tissues gradually stretched, can lead to dermal connective tissue damage, collagen fibers and elastic fibers damage, and thus the formation of chest stretch marks. 2. Hormone level changes: women in the body during pregnancy, various hormone level changes. Increased levels of glucocorticoids can inhibit the activity and proliferation of fibroblasts, which in turn reduces the synthesis of elastic fibers and collagen. This ultimately affects the repair of damaged connective tissue within the dermis. The formation of stretch marks on the chest may also be related to other causes. Women are advised to visit the dermatology department of a hospital.