Mold can grow in dark and damp areas in your home very quickly, and nowhere provides a better breeding ground for mold than carpeting. The soft fibers of your carpet can be used as a food source for the fungus, and if your carpeting is colored darkly, you may not even notice the mold growth until it has become widespread. Fortunately, there are a number of mold growth warning signs that you can keep your eyes out for to determine when you need to contact a mold remediation specialist.
One of the easiest to notice warning signs associated with mold growth is a musty, earthy or fungal smell that seems to permeate an entire area. Keep in mind that since this smell will happen slowly over time as mold grows, it may be hard to discern straight away. If guests to your house comment on a smell, however, or you smell a strange scent when coming home to your house after a few hours outside, you may want to have your carpets inspected.
Another common sign associated with significant mold growth in your home is if you notice an increase in the severity of your allergies, or any other respiratory conditions, without a corresponding reason. This can point to hidden mold growth in your carpeting which has progressed to the point of being an actual health concern. If your allergies suddenly get worse, you need to contact a professional straight away.
If you notice that there is a wet spot on your carpet, or an area that feels just slightly damp, you may have a mold problem in your carpeting (or may be about to experience one). This moisture can either be produced by the mold itself, causing a spot to develop in your carpet that is consistently moist, or can be caused by a leak in your home's plumbing or exterior that has soaked an area of the carpet. A wet area of carpet that does not currently have mold growing in it will soon experience mold growth: fixing the leak and having the carpet cleaned can help prevent this from happening.
Finally, if you've noticed any of the above symptoms, you can visually check to see if your carpet has mold growing in it (even if the carpeting material is too dark to see the mold). Simply lift your carpet up, and inspect the pad underneath: mold will quickly spread from the pile on top to the backing underneath, and will leave dark spots that can be easily visually verified.