A nice article should hit the stands soon in Lasers in Surgery and Medicine on a variable that has never been taken into account that may limit the effectiveness of laser or IPL treatments.
***Pressure applied to the superficial blood vessels when physician is trying to keep good contact with laser device and patient's skin.
This pressure can actually push blood forwards and backwards so that there is NO BLOOD (and thus no target for laser) directly under the laser tip or crystal head. This results in ineffective treeatment.
This is especially important when using gobs of topicals such as anesthetic or contact gel which makes it harder to know how much pressure you are actually applying to the skin and thus not know how much you are squooshing the blood out of the superficial hair pin loops. You can also show this phenomenon with gentle pressure by glass slides used in the laboratory.
Another problem is based on the area, especially the nose. Most doctors move the tip of the nose to get a flat surface. That in itself can cut off blood supply temporarily to the site under treatment. Also, as indicated in the article, most physicians naturally press down harder on most areas of the nose.
An interesting factor never taken into account. In conclusion, the patient should never feel anything other than the lightest touch of the laser/IPL in contact with the skin.