Earthy or Soil-Like – Similar to Wet Dirt or Leaves

Some molds smell like wet soil, rotting leaves, or a damp forest. People sometimes mistake this odor for natural “outdoor” air drifting inside.
But if the smell is strong in one spot indoors—around windows, in attics, or behind walls—it often points to hidden leaks or condensation. The CDC notes that earthy odors are strongest near water-damaged areas.

Rotten or Sour – Linked to Black Mold

Certain molds, including black mold (Stachybotrys chartarum), produce sharp, foul odors. These may smell like rotting food, sour milk, or even ammonia.
If your home smells like rotten food or animal urine without a clear source, mold may be hiding inside walls, insulation, or HVAC systems. These odors should not be ignored, as toxic mold can harm health—causing breathing issues, fatigue, or other problems.

Sweet or Fermented – Rare but Possible

Some molds smell sweet, like alcohol or spoiled fruit. People may confuse this with spilled drinks or overripe food.
These odors usually come from hidden mold colonies in kitchens, behind appliances, or in air ducts. The AIHA explains that these smells come from special gases called MVOCs, unique to certain molds. Catching them early may stop mold before it spreads further.