A Thank you for asking a very common question.
First of all I ask my patients to quit smoking at least 3 weeks prior to surgery. This is because quitting smoking is a very stressful period and should not be superimposed on the stress of recent surgery. It is better to focus on one aspect at a time. Also, if you quit a few days before, you will likely have increased sputum production and coughing which is dangerous in the immediate healing period. Coughing causes a rapid spike in venous blood pressure which could cause bleeding and a possible hematoma requiring surgical intervention.
Smoking can cause spasm of the small duct work of the lungs (bronchioles). This is similar to asthma. Sedation And anesthesia can be affected in dangerous ways by this spasm.
During the healing period, tissues have altered blood supply due to tunneling under the skin which divides some of the vascular supply. The skin is maintained with a much reduced blood supply traveling through very small vessels intimately associated with the skin. Nicotine is found in cigarette smoke, vapes, nicotine replacement patches lozenges and sprays. It is a very potent vasoconstrictor which causes blood vessels to Decrease their diameter which greatly reduces blood flow. The flaps of skin which were elevated during the procedure may have such a significant reduction of blood nourishment that it dies. This can create significant scarring and disfigurement.