The red stripes at the base of the thighs are expansion lines, also known as atrophy lines, which are lines that appear due to the body’s sudden growth or sudden fatness, so that the skin can not adapt. If more obese, lose weight too fast, the skin is too late to adapt, can also form expansion lines. In addition, sometimes the skin in the long-term topical corticosteroids, hormones can inhibit the proliferation of fibroblasts, which leads to skin elastic fibers fracture, skin and muscle atrophy, the dermis of the elastic fiber is pulled off, can also form swelling lines. Expansion lines generally tend to occur in the thigh roots, the back of the waist.