There are many reasons. This situation is mainly due to the decrease of blood oxygen content. For example, pneumonia, altitude, heart failure, asthma, pulmonary heart disease, constipation, abdominal pain and diarrhea can all be caused, and fatigue can also be caused. I suggest you go to the hospital for examination and determine the cause, so as to prescribe the right medicine.
Guiding opinions:
There are also some men whose lips are darker. If your color has changed recently, you can go to the hospital to check whether there are other abnormalities. If this has been the case, there is no need for treatment.