Who you should call depends on what the chemical smell resembles. A rotten egg odor means you should call your gas utility company immediately. A fishy or burning plastic smell means you need a licensed electrician. A sweet, chloroform-like scent points to an HVAC technician. And if the smell is strong, you feel dizzy or short of breath, or you can’t identify the source, call 911 and leave the house first.
The trick is matching the odor to the most likely source, because each one has a different professional who handles it. Here’s how to narrow it down.
Rotten Egg Smell: Call Your Gas Company
Natural gas is odorless on its own, so utility companies add a chemical called mercaptan that gives it a distinctive rotten egg smell. If you notice this odor, call your local gas company’s emergency line immediately, but do it from outside or from a neighbor’s phone. Don’t flip light switches, strike matches, use your doorbell, adjust your thermostat, or do anything that could create a spark. If the smell is strong, get everyone out of the house before making the call.
Don’t go back inside until a gas company representative inspects the home and confirms it’s safe. This service is typically free and available 24/7. Your gas bill or the company’s website will have the emergency number, or you can simply call 911 and they’ll dispatch the right responder.
One common point of confusion: sewer gas also contains sulfur compounds and can smell like rotten eggs, but it’s a more complex, organic odor, often mixed with a musty or ammonia-like quality. Natural gas smells cleaner and more “pure” by comparison. If you suspect sewer gas rather than a natural gas leak, a plumber is the right call. Dried-out drain traps, cracked sewer lines, or faulty vent pipes are the usual culprits.
Fishy or Burning Plastic Smell: Call an Electrician
A strange fishy odor near an outlet or light fixture is one of the warning signs of an electrical fire in progress. Most electrical wiring is insulated with plastic, and when components overheat, that plastic melts and produces a sharp, acrid smell that many people describe as fishy. This is not something to investigate on your own while the power is running.
Go to your breaker box and turn off the main switch to cut power to the entire house. Then call a licensed electrician and let them know you have an electrical emergency. An overheating wire or faulty connection behind a wall can ignite surrounding materials, so speed matters. In some cases the problem originates with the utility cable coming into the house rather than your internal wiring, but an electrician can locate the fault and contact the utility if needed.
Sweet Chemical Smell: Call an HVAC Technician
A sweet, almost chloroform-like odor coming from your vents or near your air conditioning unit often signals a refrigerant leak. Older systems use Freon, and newer ones use Puron, but both produce a similar sweet chemical scent when they escape. Refrigerant leaks need professional repair, both because the chemicals can be harmful in enclosed spaces and because continued leaking damages the system and can contaminate the surrounding area.
Call an HVAC technician for inspection. They’ll check coolant levels, locate the leak, and repair it. Don’t attempt to fix refrigerant lines yourself, as handling these chemicals requires certification.
Musty or Earthy Chemical Odor: Call a Mold Inspector
Not every chemical smell comes from a synthetic source. Mold, bacteria, and biofilm produce their own volatile organic compounds as metabolic byproducts. These microbial compounds create a musty, earthy, sometimes sweet odor that can fill a room and linger. The smell is the actual off-gassing of decay from biological growth hidden behind walls, under flooring, or in HVAC ducts.
If the odor is persistent, damp-smelling, and doesn’t match any of the other profiles described here, a mold remediation specialist or indoor environmental inspector is your best call. A professional indoor air quality test for a standard home typically runs $200 to $400 for basic pollutant screening, or $400 to $700 for comprehensive testing that includes mold, volatile organic compounds, and allergens. Specialized testing for individual pollutants like radon or asbestos can cost $150 to $1,000 per sample.
Unidentifiable Smell With Symptoms: Call 911
If you can’t pinpoint the source and you or anyone in the house is experiencing symptoms, treat it as an emergency. The key warning signs of dangerous chemical exposure include burning in your eyes, nose, or throat, chest tightness, difficulty breathing, wheezing, headache with dizziness, or nausea. These symptoms can indicate exposure to a range of hazardous gases, and some of the most dangerous effects develop hours after the initial exposure rather than immediately.
Severe chemical inhalation can cause fluid buildup in the lungs that doesn’t appear until 24 hours later. Headache and dizziness combined with chest pain and vomiting suggest exposure to systemic poisons. If someone in the house loses consciousness, the situation is critical.
The safest response is to leave the building immediately, taking everyone (including pets) with you, and call 911 from outside. Don’t re-enter to search for the source. Fire departments have hazmat detection equipment that can identify gases you can’t, and they’ll determine whether the building is safe to occupy.
Quick Reference by Smell Type
- Rotten eggs (clean, sharp): Gas company emergency line or 911
- Rotten eggs (complex, sewage-like): Plumber
- Fishy or burning plastic: Licensed electrician (cut power at the breaker first)
- Sweet, chloroform-like near vents: HVAC technician
- Musty, earthy, persistent dampness: Mold inspector or indoor air quality professional
- Unknown smell with physical symptoms: 911 (leave the house first)
When in doubt, err on the side of leaving the house and calling 911. Fire departments respond to odor investigations routinely, and there’s no penalty for a call that turns out to be minor. The gas company will also come out at no charge to check for leaks. These are not situations where waiting to see if the smell goes away is a safe strategy.