Raw indigo doesn't fade because the dye "wears off" evenly — it fades because of how indigo bonds to cotton in the first place. Unlike most dyes, indigo never fully penetrates the yarn core; it sits as a coating on the outer fibers, ring-dyed rather than dyed through. Every crease, every fold, every place denim rubs against a body wears that outer coating away first, exposing the undyed white core beneath.
Why whiskers form at the hips
The horizontal creases that fan out from the crotch and hip — "whiskers" in denim slang — form because that's where the fabric folds hardest and most often, every time you sit, walk, or bend. The rope-like puckering along a chain-stitched hem happens for the same reason: the chain stitch pulls the seam slightly tighter than a lockstitch would, so the fabric bunches in a soft wave that catches wear unevenly.
Honeycombs behind the knee
Behind the knee, repeated bending creates a cluster of small diagonal creases collectors call "honeycombs." They show up faster on rigid, unwashed denim because there's no stretch fiber relaxing the crease before it sets — which is part of why we still cut our core styles from 100% cotton selvedge rather than a cotton-elastane blend.
So — should you wash it?
Every wash resets some of that contrast, softening creases that took months to form. There's no universal rule, but as a starting point: if you want dramatic, high-contrast fades, hold off washing for at least the first month of regular wear, then wash cold, inside out, and air dry. If comfort and hygiene matter more to you than the fade pattern, wash whenever the jean needs it — the indigo will still fade, just more gradually and evenly.
The short version
A good fade isn't luck. It's just friction, time, and a rigid weave with nowhere to hide — recorded permanently in a coating of dye one shade at a time.