This sequence of thoughts was triggered by an observation by Prof. Peter Lee during a biomechanics class.
Many students of biology or anatomy would know that our skin’s dermis (inner layer) is a connective tissue whose largest constituent is collagen. Collagen is a type of extra-cellular protein that looks like three ropes wound around each other at microscopic level. Two interesting facts about skin and collagen are in order: 1) Skin is the largest connective tissue and the largest organ of our body. 2) Collagen is the second most (after meat) animal produce consumed by human beings (if you exclude milk). All of the gelatin used in in food, pharmaceutical, photography, and cosmetic industry comes from animal connective tissues.
During the class, we came to know that the strings of collagen permanently orient themselves along specific directions. This orientation of collagen produces cleavage lines on the surface of skin, and that is what gives rise to all lines seen on our skin. These lines are the cause of wrinkles at elder age. In fact, only few parts of our body do not have clearly defined cleavages and our skin is *stretched* all the time along these lines.
These lines (sort of field lines of a very complex electric or magnetic field) were first mapped out by an Austrian anatomist Carl Langer (1819-1887). He systematically made fine cuts on the cadaver skin and observed in which direction the cuts elongate. The direction of elongation reveals the direction in which the skin is stretched and hence the orientation of underlying collagen. These lines of tension on skin are named after him as Langer’s lines.
Here is what these lines look like..
If you experience a cut along the Langer’s lines, the scar will not be very visible and the wound will heal fast. But if the cut is perpendicular to the Langer’s lines, the wound will tend to open up and the scar will be more visible. Surgeon’s (especially those involved in plastic surgery and beauty services) must respect these lines when making incisions on patient’s skin.
And perhaps these lines are the reason (as Prof. Lee remarked) wives ask their husbands to rub moisturizer on their face not randomly but along certain directions 
Any comments from ladies? Do you think the lines in the image above are preferred directions for rubbing creams?
Posted by Shalin Mehta 
