Age

• Infants, who have immature immune systems, and preschoolers have not developed the antibodies to many of the 200 viruses that cause colds. Kids catch a lot of colds, and are not usually careful about sneezing or nose-blowing.
  
  

Proximity to Others

• Day care, school, and shared office space all contribute to the risk of catching a cold. Likewise, travel by bus, airplane, subways, or trains increases your chance of infection.
  
  

Stress

• Researchers at Carnegie Mellon University in Pennsylvania found that people with higher stress levels were twice as likely to catch a cold than those with less stress levels.
  
  

Poor Hygiene

• Not washing your hands, especially if you are exposed to sick people, is an easy way to catch or spread a cold. Sharing cups or utensils also increases your risk.
  
  

Environmental Exposures

• The airways of smokers may already be damaged or inflamed, making it easier for cold viruses to settle in. This is also true of kids and others exposed to secondhand smoke. Smoggy air may also have the same effect.
  
  

Chronic Conditions

• People with chronic health or immunocompromised conditions are more susceptible to the virus. The cold may also last longer, be more severe, or lead to dangerous complications like pneumonia.