A mushroom-shaped tip on a candle wick is carbon buildup at the end of the wick. It can occur as a candle burns and does not automatically mean the candle is defective.
Why does buildup happen?
Combustion conditions, wick characteristics, fragrance, wax and burn behavior can all influence carbon buildup. What matters most is how the candle is actually burning.
What should you do?
Extinguish the candle before trimming. Once the candle and wick are cool enough to handle safely, trim the wick according to the candle's care instructions before the next burn. Keep wick debris out of the wax.
Watch the flame, not just the wick shape
If the candle develops an unusually high flame, persistent smoking, excessive soot or another unsafe burn condition, extinguish it and follow the warning label.
For a broader care checklist, see 9 Candle Mistakes to Avoid.