Obesity lines are formed because the volume of bones and muscles or fat increases too fast, exceeding the extension speed of skin, and the elastic fibers of dermis are pulled off. People who gain too much weight can see this situation, and many developing people can appear even if their weight gain is not obvious. Even if you lose weight successfully and return to your original body shape, it will be red at first, gradually darken with time, and finally become white stripes.

The above is a suggestion on the question "Will thin people grow fat lines?". I hope it helps you, and I wish you health!