[pct-l] Blisters

[CHUCK CHELIN]

Good morning,

I entirely agree that shear failure of subcutaneous layers is the most
common cause of blisters, but there is a closely-related failure mode that
can produce a similar blister.   Even if the fit of the shoe and the habits
of the walker are such that (almost) no slippage exists there can still be
a problem, typically on the bottom of the heel or under the ball of the
forefoot.  A walking load repeatedly applied directly onto a limited area
of the foot can create a compression failure by crushing the bond between
the skin layers, creating a similar blister.

I rarely have blisters, but if I walk for miles on pavement, or on any
other hard and consistent surface, I’m at risk.  I can encourage the same
risk when I walk distances with hard-soled shoes or boots.  I find that
boots are particularly bad in this regard because the relatively high top
guides my foot to strike the same place on the insole at every step.

If I must walk along a road, I try to spend as much time as I can on the
unpaved shoulder where the surface – while probably rougher – is likely to
be more cushioning, and it will be irregular to more widely distribute the
load across the bottom of my foot.

I believe the cause of any blister is probably a combination of both shear
and compression, in varying proportions, acting at the same time.

Once the skin bond has been broken – due to either shear or compression
failure – the result will be fluid leakage into the space between the
separated skin layers.  This fluid forms a prominent blister, subsequent
walking on the blister will cause hydraulic force to act towards the side
of the blister further separating the skin layers.  More separation means
even more fluid leakage, and still more hydraulic separation, etc.

My answers are: 1) Conditioning by regularly walking until I’m foot-sore
but not blistered.  2) Stopping immediately when I feel a hot-spot to
reinforce the skin with tape before a blister forms.  3) If a blister has
formed, I fix it immediately before the skin above the blister tears. 4) I
remove the fluid from any blister that forms to stop the hydraulic
separation. 5) Next, I apply tape to a large area around the blister to
reinforce the shear strength of the skin above the local area.  6) Finally,
I may add thicknesses of tape or moleskin to remove the greatest force from
the center of the blister by transferring it to adjacent, more
lightly-loaded areas.

It is difficult to keep tape attached to skin -- particularly sweaty, oily
skin.  I don’t carry any special tape preparation product, so I just use
fuel alcohol to clean the taped area.  Not only will the alcohol clean the
area and dissolve excess oil, but it also has a great affinity for water to
dry the area for better tape adhesion.  Even if I’m not cooking, I may
carry about one-half ounce of alcohol through the early days of a long hike
just for this purpose.  I also find that the tape remains in place longer
if I use larger pieces to locate the edges of the tape aside into areas
where the contact force is less; particularly edges that are perpendicular
to the direction of rubbing.

I keep my feet as dry as I reasonably can because that is the most
healthful and comfortable thing to do, but I don’t think that moisture is
the prime cause of blisters.  I have hiked for miles and days with wet feet
and had no blisters.  Similarly, I don’t believe heat is the cause.  Some
of the most foot-scorching days caused no blisters, while I have gotten
blisters when my feet were so cold I couldn’t feel them forming.

Steel-Eye

-Hiking the Pct since before it was the PCT – 1965

http://www.trailjournals.com/steel-eye

http://www.trailjournals.com/SteelEye09/