Skew from zero
1/4What is skew?
If Black-Scholes were literally true, every strike would trade at the same implied volatility. They don't. Skew is the pattern of how IV varies across strikes at a single expiry.
Picture a row of options all expiring on the same date. Each has its own IV. Line them up from low strikes (OTM puts) to high strikes (OTM calls). The shape you get is the volatility smile or smirk — and the tilt of that shape is skew.
The most common pattern: OTM puts trade at higher IV than OTM calls. That tilt is called put skew. It means the market charges more for downside protection than for upside speculation.
Think of insurance pricing. Flood insurance in a floodplain costs more than fire insurance in a fire-proof building. Skew is the options market saying "crash risk is more expensive than rally risk" — because crashes are more damaging and happen faster.
Why put skew exists
Skew is not a quirk. It reflects real structural forces in the market: who needs protection, who is willing to sell it, and how markets actually move.
Force 1: Crashes are fast, rallies are slow. Markets don't move symmetrically. Drops are violent — multi-sigma moves happen in hours. Rallies tend to grind higher over weeks. Historical return distributions are negatively skewed.
Force 2: Everyone wants crash insurance. Portfolio managers, funds, and retail traders all buy OTM puts to hedge downside. Very few are natural sellers of puts — it's risky to be short crash insurance. This supply-demand imbalance pushes put IV up.
Force 3: Volatility rises when prices fall. When a stock drops, its debt-to-equity ratio increases, making it riskier. This "leverage effect" means realized vol increases in selloffs, validating the higher IV that puts were pricing in.
Reading skew levels
Traders don't just eyeball the smile — they use a standardized metric called the 25-delta risk reversal to put a number on skew.
Why delta instead of strikes? A $90k put means very different things depending on where spot is. Delta standardizes moneyness — a 25-delta option is always roughly the same "distance" from ATM in probability terms, regardless of spot price or volatility level.
Quick reference:
+15 or more — extreme put skew, panic mode+5 to +15 — elevated put skew, nervous market0 to +5 — mild put skew, normal conditions-5 to 0 — flat, no strong directional fearbelow -5 — call skew, upside FOMO (rare)
Move the skew slider above and watch the 25Δ Risk Reversal metric update. Notice how the red dot (25Δ put IV) and blue dot (25Δ call IV) diverge as skew increases.
Skew as a signal
Skew isn't static. It moves with market conditions — and those moves contain tradeable information.
Sharp selloff: Put skew steepens. Hedging demand spikes, fear increases. The 25d RR jumps.
Slow grind up: Put skew flattens. Fear subsides, put sellers emerge, skew compresses back toward normal.
Pre-event (FOMC, ETF decision): Both wings elevate — the smile becomes more pronounced. The market expects a big move but doesn't know which direction.
Post-event: Wings collapse, skew normalizes. The uncertainty that justified the premium has resolved.
In equities, put skew is strong and persistent — it rarely flips. In crypto, skew can flip from put-heavy to call-heavy within days during a regime change. Crypto skew mean-reverts in days to weeks; equity skew takes weeks to months.
Trading implications:
Buying OTM puts is expensive because of skew premium — you're paying above "fair" for crash insurance. Selling OTM puts collects that premium, but you're short tail risk. Some traders trade skew directly via risk reversals (sell puts, buy calls, or vice versa), betting on skew flattening or steepening without a directional view.
Where to go next:
Term structure — the time dimension of volatility
Vol surface — combining skew and term structure into the full picture
Skew course lesson — the full course module