The constricting effect that smoking and nicotine have on blood vessels starts to let up when you stop smoking, improving the delivery of nutrients and oxygen to the skin cells, allowing them to repair properly. As nicotine also increases the stickiness of the platelets in the blood, it can lead to obstructions, further reducing oxygen delivery to the cells. Combined with carbon monoxide and hydrogen cyanide - both found in tobacco smoke - they inhibit the transport and metabolism of oxygen in the blood and in the cells, making wounds heal slower and less effectively. Quitting tobacco will see your body taking care of skin much damage faster, and reduces the risk of scarring.