Mold HQ
Moisture first. Mold second.

Mold starts as moisture. Learn to see it early.

A water stain, a musty closet, a window that sweats every morning. Most mold problems give warnings long before anything grows, and once materials get wet from a leak or flood, mold can start in as little as 24–48 hours. We'll show you where to look and what it means, so you can catch problems early.

Get the room-by-room guide See the warning signs
Who we are

Built by people who work in mold every day

We're professionals from the mold and environmental industry. In our work, the same story comes up again and again: the warning signs were there long before anyone noticed them.

Mold HQ puts that field experience in your hands. Our room-by-room guide shows you where moisture problems usually start. The tools we recommend and products from our partners are here to educate and empower anyone who wants to know more about what's going on in their home.

And when something needs a closer look, we'll help you recognize when it's time to call a professional.

Warning signs

Signs of moisture intrusion

Mold feeds on organic material that's already in every home, from the dust that settles on surfaces to the paper on drywall and wallpaper. What it needs to grow and spread is water. None of these signs mean you have mold, but each one means water is somewhere it shouldn't be, and that creates the right environment for mold.

  • Musty or earthy odor

    Often the first clue, especially in closets, basements, and under sinks. Your nose can find what you can't see.

  • Window condensation

    Regular sweating on glass or frames points to high indoor humidity, not just a cold morning.

  • Stains and rings

    Yellow or brown rings on ceilings and drywall mark where water has traveled, even if it's dry now.

  • Bubbling or peeling paint

    Moisture pushing through a wall lifts paint and wallpaper from behind.

  • Warped wood and baseboards

    Swelling, cupping, or soft spots in flooring and trim mean wood has absorbed water.

  • White, chalky deposits

    Efflorescence on concrete or brick shows water is wicking through foundation walls.
The Mold HQ Guide

A room-by-room walkthrough of your home

Once you know the signs, the next step is knowing where to look. Every area of a home has its own problem spots, and the full guide walks through each one with interactive plans, explanations of where the moisture comes from, and checklists. Here's a preview of why each area is a concern.

$25

A comprehensive, interactive guide that maps out typical home features and the spots that often go unchecked, with a checklist for every area.

Buy the guide
Recommended tools

Tools for keeping an eye on and controlling moisture

You don't need professional equipment to notice changes in your home. These tools help you check humidity and moisture as you work through the guide.

Measures % RH

Hygrometer

Tells you your indoor humidity. Check readings in different rooms and through the seasons.

Measures % MC

Moisture meter

Checks how wet drywall, baseboards, cabinetry, and sills are. Compare a suspect spot against a dry spot nearby.

Controls % RH

Dehumidifier

Pulls humidity down in poorly ventilated areas so mold doesn't get the conditions it needs.

Finds temperature differences

Thermal camera

Shows cool spots where evaporating water may be hiding behind walls and ceilings. Confirm any finding with a moisture meter.

Prevention

Keep moisture from building up in the first place

Mold needs moisture to grow. A few everyday habits keep humidity in check and stop most problems before they start.

  • Bath
    Run the exhaust fan during and after showersKeep it on for 20–30 minutes after you're done. If the mirror is still fogged, the fan isn't keeping up.
  • Air
    Open windows and keep air movingCrack a window when cooking or showering, keep interior doors open, and pull furniture a few inches off exterior walls.
  • RH
    Watch your humidityHumidity naturally changes with your climate and the seasons. What matters is a room that stays noticeably more humid than the rest of the house, or humidity that stays high long after showering or cooking.
  • Damp
    Dehumidify closets and windowless roomsA dehumidifier pulls humidity down where ventilation alone can't, especially in summer.
  • 24–48h
    Dry spills and leaks fastWet materials that dry within a day or two rarely grow mold. Fix drips under sinks and around toilets right away.
Govee · Hygrometer

Govee Bluetooth Hygrometer Thermometer

Shows a room's humidity at a glance. Put one in the bathroom and one in a closet or windowless room.

View on Govee
Govee · Hygrometer

Govee Wi-Fi Thermo-Hygrometer

Check humidity from your phone, even when you're away from home.

View on Govee
Govee · Leak detection

GoveeLife Water Leak Detector 1s

Place under sinks, behind toilets, and next to the water heater to catch leaks early.

View on Govee

We earn a commission on products linked in this section.

Testing

Mail-in test kits and sampling gear

Already seeing signs and want to know more? In-home test kits from our partner HomeSAFE let you collect samples and send them to a lab for analysis.

Mold test kit

Identifies common indoor molds, including Aspergillus, Penicillium, and Stachybotrys.

  • 2 microbial testing swabs
  • Step-by-step instructions
  • Sampling form
  • HomeSAFE bubble mailer for return
Order from HomeSAFE

Asbestos test kit

Tests suspect building materials for asbestos.

  • 2 individual sample bags
  • Step-by-step sampling instructions
  • Sampling form
  • Transport bag for shipping
Order from HomeSAFE

Asbestos test kit 5 pack

Checks more suspect building materials before renovation, repair, or removal work. Also available as a 10 pack.

  • Five individual sample bags
  • Step-by-step sampling instructions
  • Large transport bag for samples and paperwork
Order from HomeSAFE

Lead dust and debris wipe kit

Measures the amount of lead collected from a sampled surface. Available with 1, 2, or 3 wipes.

  • Lead dust sampling wipe
  • Sample tube
  • Pair of disposable gloves
  • Step-by-step sampling instructions
  • Reusable shipping box
Order from HomeSAFE

N95 respirator and gloves bundle

Protective gear for at-home sampling. Not intended for asbestos removal or other high-risk work.

  • NIOSH-approved N95 respirator
  • Pair of disposable nitrile gloves
  • Also available as a 2 pack
Shop on HomeSAFE

HomeSAFE is our sampling partner, and we earn a commission on kits ordered through our links. Lab results show only what was sampled and aren't a diagnosis of your home.

  1. Order your kit
  2. Collect samples
  3. Mail to the lab
  4. Get your results
Next steps

When to call a professional

The guide, tools, and test kits help you spot problems. A qualified mold professional can find the source, determine the extent, and recommend how to fix it.

  • Your test results come back identifying mold or active growth
  • Visible growth that can't easily be wiped away or keeps coming back
  • Water damage from a flood, sewage backup, or long-running leak
  • A musty odor you can't trace, or one that keeps coming back
  • Moisture readings that stay high after you've dried the area
  • Anyone in the home with health concerns. Talk to a doctor too.
  • You need a documented professional inspection report