Monday, March 29, 2010

Zit Vac

Whether it was the prom, a first date, or an important job interview, everyone’s had some special event ruined by a zit.  For times like these, it’d be great if there were a Hoover vacuum1 attachment that could suck the pore open again.  Is this physically possible?  How much of a pressure difference would you need to vacuum off a zit?

Many zits can be popped with just your fingers, but we’re really interested in the diffcult-to-pop zits2.  For that reason, we’ll consider zits that are at least as strong than as the maximum force our fingers can produce.  It’s difficult to know one’s finger strength a priori, but this site suggests that a healthy thumb should produce a maximum force of about 200 N while a healthy index finger may produce 100 N of force.  This force squeezes on the zit causing the internal pressure to increase and the skin to deform.  The deformation may absorb some of the force so that the pressure inside the zit is less than it would be otherwise.  For simplicity, I’m going to neglect this effect and assume the force gets applied directly to the zit over an area of about 0.25 cm2.  From this, we can estimate the pressure needed to pop a zit.

pressure = (total force) / (area)
= (300 N) / (0.25 cm2)
= 1.2 ×107 Pa.

That’s about 2000 psi3.  It’s also about 120 times larger than atmospheric pressure, meaning that even with a perfect vacuum there’s no way to build up enough of a pressure difference for this to work4.  This makes intuitive sense as anyone who’s tried to vacuum a zit off can tell you.

[1] I imagine it will look something like that tube at the dentist’s office that sucks up your face.
[2] Why use a Hoover attachment when you can just use your fingers?
[3] Good call, Boomer!
[4] Mr. Wizard did an experiment similar to this where they tried to see how far you could suck water up a straw.  I’ve been unable to find video of this online, but here’s one just for nostalgia’s sake.


  1. Roughly the pressure of two fingers pressing hard on either side of a zit. Say, 25 psi?

  2. Um if the zit is squeezed between an index finger and a thumb the maximum force it could be exposed to is 100 N not 300. The index finger would apply the force and the thumb is there to provide a reaction force.