The short answer

Candles smoke after they're blown out because the wax is still hot enough to vaporize, but there's no flame to burn it off.

The long answer

Let's begin with how candles work.

A candles are made up of two parts: wax and a wick. The purpose of a wick is to keep a flame going which causes the solid wax to turn into liquid wax. This liquid wax is then absorbed by the wick where it heats up further and turns into vaporized wax. The vaporized wax is flammable and this constant fuel source is what keeps the candle lit.

Smoke is made up of the unburned carbon particles released when the candle wax breaks down. There is no smoke while a candle is burning because most of the carbon in the vaporized wax gets burned.

But when the flame is blown out, the wax is still hot enough to form a vapor but there's nothing to burn off carbon, resulting in smoke. A candle smokes when you blow it out because there is still heat to vaporize wax.

The best way to blow out a candle without smoke is to push the burning wick into the melted wax, using a candle wick dipper. The hot wax will immediately put out the flame.

🧠 Bonus brain points (or just a fun party trick)

You can relight the candle shortly after you blow it out by placing a flame in the smoke.

Sources

American Chemical Society. (2021, December 24). The Science of How a Candle Burns. YouTube. Retrieved January 14, 2023, from https://www.youtube.com/watch?v=B9asozzeAwY

Carl. (2021, October 27). Why Do Candles Smoke When Blown Out? Candleers Candle Co. Retrieved January 14, 2023, from https://www.candleers.com/why-do-candles-smoke-when-blown-out/

Villazon, L. (2020, April 21). Why do candles only smoke after they've been extinguished? BBC Science Focus Magazine. Retrieved January 14, 2023, from https://www.sciencefocus.com/science/why-do-candles-only-smoke-after-theyve-been-extinguished/