The main difference between mucus and phlegm relates to where each substance comes from. Mucus normally comes from a person's mucous membranes, such as from inside the nose, while phlegm usually comes from the back of the throat or lungs. While both substances are slippery in texture, phlegm is typically thicker than mucus. People who have colds normally blow mucus out of their noses and might cough up phlegm from their throats or lungs.
Both of these substances are usually present inside the body at all times, but they may become more abundant when a person has a cold or his allergies act up. The excess tends to make colds and allergies much more uncomfortable for people who suffer from them because increased nose-blowing and coughing may be necessary. Another difference between mucus and phlegm is that phlegm often contains dead bacteria, virus, and white blood cells. It might also appear more congealed than mucus does. Even though it may be tempting to swallow it, many healthcare professionals advise people to cough up phlegm when it rises in their throats because doing this may help to rid their bodies of whatever infection they might have.
Expelling either may be particularly problematic at night when a person is trying to sleep, and both of these substances can interfere with normal sleeping patterns. Medical professionals often recommend or prescribe cough suppressants to help people who are producing lots of mucus and phlegm to sleep better. Cough suppressants are typically recommended for use only at night because coughing is one of the ways in which a person's body rids itself of infections. Coughing during the day when a person is awake and not trying to get to sleep may be beneficial.
Medical professionals occasionally prescribe cough expectorants for people to use during the day to help them cough up more phlegm. Some people with colds may have problems with dry coughing, which is also described as a cough that doesn't produce much mucus or phlegm. Dry coughs are normally unproductive and might cause extreme throat irritation that could lead to hoarseness when a person tries to talk. During the day, an expectorant may be very helpful for a person who is sick to expel from her nasal passages, throat, or lungs.