Wet Areas

• Wet areas that do not dry well or completely tend to have a foul, sour smell to them. This is especially true if mold growth or mildew develops along with the moisture. If you have a sour smell in your home, check the residence thoroughly for wet areas, leaks or other sources of moisture that could be allowing an area to stay too wet and develop the sour odor.
  
  

Food and Drink

• One of the most common causes of bad or sour odors in a home is spoiled food. Some foodstuffs, such as dairy products, are especially likely to create a sour odor if left out too long, spilled and not cleaned up, or simply forgotten about. Check your kitchen and dining area for bad or old food products you may have forgotten about or not used in time. Households with children are especially likely to experience this problem, as children may not always tell you when they misplace or spill a bottle or cup full of milk or juice.
  
  

Ventiliation

• A sour smell is more likely to develop in an area with poor or no ventilation. Areas that are not used or cleaned regularly tend to become stagnant and may create a slightly stale, sour odor. This is also true of old, unused or not regularly cleaned furniture and bedding as well. If the sour smell seems to be coming from your heating or air conditioning system, you may need to clean your ducts, furnace or filters.
  
  

People and Pets

• Hygiene is important for both humans and animals. Sour odors can develop if people or animals are not maintaining good hygiene practices, especially during hot temperatures when people sweat a lot. Sweat has a sour odor to it, especially if sweaty clothing is allowed to sit in a laundry hamper or if dirty laundry is allowed to build up in the home. In some cases, sour odors coming from a person can also be a sign of illness or a health condition.