Warts can occur almost anywhere on the body, but a wart on the sole of the foot behaves very differently from a wart on the hand, finger or top of the foot.

Although they are caused by the same family of viruses human papillomavirus (HPV), their location and the type of skin in which they develop can make a significant difference to how we treat them.

At Dubai Podiatry Centre, we often see patients who have already tried traditional wart treatments such as salicylic acid or liquid nitrogen on a plantar wart, sometimes repeatedly, without understanding why a treatment that may work very well on a wart elsewhere on the body can be much less effective on the sole of the foot.

The simplest way to understand this is to think about how much of the wart we can actually reach.

Warts Elsewhere on the Body: Think of a Water Balloon

Imagine a small water balloon sitting on a table.

Most of the balloon is above the table. If you wanted to paint its surface, you could probably cover around 90% of it quite easily. Only the small area touching the table would be difficult to reach.

A wart growing outward from the skin can be thought of in a similar way.

On areas such as the hand, finger or top of the foot, a wart may project outward from the surface. This means that a large proportion of the wart is directly accessible to treatment.

This is one reason why traditional surface treatments can work particularly well in these locations.

Salicylic Acid

One of the simplest and most widely available wart treatments is salicylic acid.

Salicylic acid is a keratolytic, which means that it breaks down keratin and gradually removes the thickened, virus infected skin cells.

It is available from pharmacies in several forms. It may come as a liquid that looks rather like clear nail polish and is painted directly onto the wart, or it may be incorporated into a medicated plaster or padded dressing that keeps the treatment against the affected skin.

When much of the wart is projecting outward, there is a relatively large surface area available for the medication to act upon.

Liquid Nitrogen

Another commonly used treatment is cryotherapy, usually with liquid nitrogen.

The wart tissue is rapidly frozen, damaging the infected cells and encouraging the body’s immune response against the virus.

Again, when the wart projects outward from the skin, the treatment can be applied directly to a substantial proportion of the affected tissue.

Plantar Warts Are Different

A plantar wart, sometimes called a verruca, develops on the weight bearing skin of the sole of the foot.

Here, the situation is almost the reverse of our water balloon example.

Instead of most of the lesion projecting outward where we can easily treat it, much of the plantar wart can become embedded within thickened plantar skin.

Standing and walking also continually place pressure on the lesion. Rather than being able to expand freely outward, the wart becomes compressed within the thick keratinised layers of the sole.

This means that what we see on the surface may represent only a relatively small part of the affected tissue.

The 90% versus 10% analogy is a useful way of visualising this difference: with an outward growing wart, most of the lesion may be readily accessible to treatment, whereas with a plantar wart, much more of the affected tissue may lie beneath the visible surface.

These percentages are an analogy rather than a literal anatomical measurement, but they help explain why treatment results from warts elsewhere on the body should not automatically be applied to plantar warts.

Why Is the Skin on the Sole So Different?

Another useful way to understand this is to imagine fish scales.

Under magnification, the outermost layer of our skin consists of flattened keratinised cells arranged together to create a protective barrier.

For a simple visual analogy, imagine the delicate scales of a little goldfish. This represents the relatively thinner epidermis found over much of the body.

Now compare those with the much tougher protective scales you might imagine on a very large fish.

That is closer to how we can think about the specialised thick skin on the soles of our feet.

The plantar surface has a particularly thick outer keratin layer because it has to withstand enormous amounts of pressure, friction and repeated loading throughout our lives.

That protection is extremely useful for walking but it presents a challenge when treating a plantar wart.

When HPV infects the skin elsewhere on the body, the resulting wart may be able to proliferate outward relatively easily.

On the sole, however, the combination of the thick stratum corneum and pressure from standing and walking means that the lesion tends to become incorporated into the thickened plantar skin rather than simply projecting outward.

Why We Use Dermojet for Plantar Warts

This difference in anatomy is one of the reasons we use Dermojet treatment for selected plantar warts at Dubai Podiatry Centre.

A Dermojet is a needle free, high pressure jet injection device. Rather than relying purely upon a treatment being placed onto the external surface of the wart, it allows medication to be delivered through the thick plantar skin into the targeted tissue.

This is particularly useful on the sole of the foot, where the thick outer layer of skin can otherwise act as a substantial barrier.

The aim is therefore very different from simply painting or freezing what can be seen at the surface.

Why We Would Not Automatically Use the Same Approach Elsewhere

Treatment should always be chosen according to the location and characteristics of the wart.

If a wart is projecting outward from thinner skin elsewhere on the body, much of the affected tissue is already accessible from the surface. Treatments such as salicylic acid or cryotherapy may therefore be more appropriate.

A high pressure delivery system designed to penetrate thick plantar skin would not automatically be the appropriate choice for an outward projecting wart elsewhere on the body.

This is why there should not be a one treatment fits all approach to warts.

Same Virus, Very Different Environment

The important point is that a plantar wart is not necessarily difficult to treat simply because the virus itself is different.

It is the environment in which the wart is growing that changes.

The sole of the foot has:

• exceptionally thick keratinised skin
• repeated pressure from standing and walking
• friction and compression
• a substantial protective stratum corneum
• different accessibility compared with an outward projecting wart elsewhere on the body

Understanding these differences helps us choose a treatment that is appropriate for the anatomy rather than simply treating every wart in exactly the same way.

The Water Balloon Rule

A simple way to remember it is this:

Wart projecting outward:
Think of a water balloon sitting on a table. Most of it is exposed and accessible, so a surface treatment can reach a large proportion of the lesion.

Plantar wart on the sole:
Think of the balloon being pushed down into a thick, tough surface. Much less is visible and accessible from above, so treatment may need to address tissue beneath the superficial keratin.

At Dubai Podiatry Centre, this anatomical difference is an important consideration when assessing plantar warts and deciding which treatment approach is most appropriate for each patient.

Warts should be properly assessed before treatment, particularly if a lesion is painful, bleeding, changing in appearance, persistent, or if there is uncertainty about whether it is actually a wart.

 

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