The red stripes on the inner thighs are usually expansion lines, also called atrophy lines. The principle of its onset is the same as that of stretch marks, generally related to short-term fattening or growing taller, fattening or growing taller leads to the stretching and breaking of skin elastic fibers, mainly manifesting as parallel red stripes, which may be slightly concave in the middle and soft to the touch, generally without any conscious symptoms. This condition generally does not require treatment, over time this red stripe will gradually become skin color or light white. If you feel that it affects your appearance, you can try topical application of mucopolysaccharide polysulfate cream with fractional laser treatment.