As previously mentioned, mucus gets thicker and stickier when you are sick, which is why you constantly blow your nose and hock back ‘loogies’ when you have a cold, a sinus infection or the flu.
It can also change consistency when your body is affected by an allergen and it is trying to protect your body from the allergen. Believe it or not, there are also certain foods that can cause you to create more mucus.