Why do horizontal stripes sometimes make people look thinner?

Answer: They create many edges that break up the body's outline

They stretch the fabric so it hugs the body more tightly — Wrong. Fabric doesn't stretch just because of stripes; the material behaves the same regardless of pattern. The effect is purely visual, not physical. If stripes stretched fabric, they would also change the fit, which doesn't happen.

They create many edges that break up the body's outline ✓ — Correct! The brain judges width from how many edges cross the body, and horizontal stripes add many edges that fragment the outline, so the body reads as narrower. This is the Helmholtz illusion, where a filled space looks smaller than an empty one of the same size. So stripes can slim, contrary to popular belief.

They confuse the camera into recording a narrower shape — Wrong. Cameras record light, not interpret patterns. The illusion happens in your brain, not in the lens. While camera angles can affect how stripes look, the core reason is neural processing, not photographic trickery.