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Getting to the Bottom of Common Foot Problems

W. Steven Pray, PhD, DPh
Bernhardt Professor, Nonprescription Products and Devices
College of Pharmacy
Southwestern Oklahoma State University

Weatherford, Oklahoma



10/21/2009

US Pharm. 2009;34(10):11-27. 

Pharmacists answer numerous questions and concerns patients have about a wide range of foot problems. It is understandable that the feet cause a great deal of discomfort for millions of U.S. citizens, in light of the forces that assail them in the average day. If a patient weighs just 150 lb, a short walk of 1 mile requires each foot to endure 60 tons of force.1 Of course, many patients walk far more than that in their daily activities, multiplying the potential damage to the feet by factors of perhaps 10 or more. Thus, patients request relief of corns, calluses, bunions, ingrown toenails, tired feet, sore feet, and cracked heels. This discussion will focus primarily on two of the most common problems encountered—corns and calluses. 

The Obesity Epidemic and Feet

It is no secret that the United States is in the middle of an overwhelming epidemic of obesity. As a result, the hips, legs, and feet suffer the effects of carrying obese individuals to and fro. A study of overweight and obese children confirmed that they experience a greater number of musculoskeletal problems in general, and lower extremity problems in particular, than their normal-weight counterparts.2 As it is unlikely that a nationwide thrust to lose weight will ever materialize or be successful, the pharmacist of the future is likely to counsel an ever-growing number of patients with foot problems. 

Corns

Corns are one of the more common foot problems, being localized areas of hyperkeratosis, or excess growth of the upper, keratinized layer of skin.3-5 The driving forces that induce growth of the corn are pressure and friction in specific areas of the feet, most commonly over bony prominences, such as the condyles of the heads and bases of the metatarsals and phalanges.1,6,7 The pressure and friction arise when the shoe or another part of the foot (e.g., an adjoining toe) rubs the area repeatedly during the normal activities of daily living, such as walking. 

The risk of developing corns increases with aging.1 There are at least two explanations for this epidemiologic observation. One is a general atrophy of adipose tissues with aging. Since adipose tissue cushions the foot, its loss predisposes the patient to corns. A second explanation is that feet often distort with age, manifesting as a downward displacement of the metatarsal heads. This deformity increases the pressure on the skin between those displaced metatarsal heads and the sole of the shoe, further increasing the risk of corns. 

The appearance of corns varies according to the type.1,8 Corns occur most commonly in two forms, the hard corn (heloma durum) and the soft corn (heloma molle). The hard corn is a hyper keratosis that appears like a cone or dome, with a translucent core. Hard corns range in size from as small as a pencil eraser to larger than a dime. They are most often due to ill-fitting footwear and occur in such places as the side of the small toe, an area that bears much pressure during walking. The presence of a corn in such an area causes discomfort whenever the shoe contacts it. Some patients with fully developed lateral fifth-toe corns require surgery to relieve the pain.9 

By contrast, the soft corn is usually due to the pressure of one toe against another as the toes are forced into shoes that are too narrow.1,8 These corns appear between the toes where metatarsal bones and phalanges are in constant apposition during ambulation and are also known as interdigital corns. The most common site is between the fourth and fifth toe. Patients may require surgical removal of interdigital fifth-toe corns to gain relief.9 

Patients occasionally complain of plantar corns that develop on the sole of the foot. These can cause great pain during ambulation.1 Patients may think they are plantar warts because of the pain, but they are not viral in origin.

OTC Treatment With Salicylic Acid: Corns will continue to cause pain and discomfort until they are removed, but they can be successfully treated with nonprescription products in many instances. The only ingredient proven safe and effective for unsupervised self-use is salicylic acid. It is a keratolytic, softening and destroying the outermost layer of epidermis.10-12 Its action is partly due to lowering the pH of the stratum corneum, which causes it to swell, soften, and ultimately be shed. The topical delivery system in which salicylic acid is incorporated also increases hydration of the stratum corneum, which induces damaging maceration and contributes to the agent’s efficacy. 

Salicylic acid is available for treatment of corns in flexible collodions, adhesive-backed plasters, disks, and rubber-based vehicles.1 Salicylic acid is safe and effective in concentrations of 12% to 17.6% when placed in collodions. The flexible collodion vehicle is composed of pyroxylin (nitrocellulose) in a mixture of ether and alcohol, and also contains plasticizers and other ingredients such as castor oil. After application, the ether and alcohol evaporate, leaving a flexible, water-repellent film that adheres tightly to the skin, retarding evaporation and inducing maceration. These products include Dr. Scholl’s Liquid Corn/Callus Remover, Freezone Corn and Callus Remover, and Mosco Liquid Callus & Corn Remover. 

To use a flexible collodion, the patient should first wash the affected foot and soak it in warm water for 5 minutes. This step helps hydrate the stratum corneum, facilitating eventual breakdown of the corn. The foot is then dried thoroughly. The collodion is applied carefully one drop at a time until the corn is covered. It should not be allowed to contact surrounding healthy skin. If it does accidentally reach healthy skin, the patient should remove it with a disposable tissue or paper towel. The product should be allowed to dry naturally, which should take only a minute or two. As it dries, it will assume the white appearance of dried collodion. Application should be repeated once to twice daily for up to 14 days. Some products also contain protective adhesive pads that can be placed over the corn during treatment to provide a small degree of cushioning for pain relief. 

Collodions are highly flammable, so patients should be instructed not to use them around an open flame. Patients should refrain from inhaling the volatile ingredients to prevent illness. Patients should be instructed to close the bottle as quickly and tightly as possible. If they do not, evaporation will occur inside of the bottle, causing the product’s concentration to slowly increase. Eventually, the patient may notice that the product has become overly viscous and/or that salicylic acid has begun to precipitate in the bottle. The pharmacist should instruct patients to never use a product that is excessively thick or has developed visible crystallization in the bottle. 

Salicylic acid–impregnated plasters, disks, and rubber-based products may be preferred for corn treatment.1 They contain salicylic acid in concentrations of 12% to 40%. Virtually all are adhesive backed, facilitating the patient’s goal of placing them directly over the corn. They help retain water in the stratum corneum to some degree, although perhaps not as effectively as the collodions are able to do. To use these products, the patient is instructed to wash, presoak, and dry the foot in the same manner as when using collodions. The plaster or disk is cut to size if needed. The adhesive backing is removed, and the product is applied to the corn. If the disk comes with a cover, it is applied last. The product is left on for 48 hours, and a new one is applied every 48 hours for up to 14 days, or less if the corn is removed earlier. These products include Dr. Scholl’s Corn Removers and Dr. Scholl’s OneStep Corn Removers. 

If the patient has diabetes or poor circulation, salicylic acid is prohibited in order to prevent serious complications.1 Its use should be avoided in patients with skin that is irritated, infected, or reddened. If the problem persists after 14 days, the patient should be instructed to see a physician or podiatrist. If a collodion-based product contacts the eyes, the patient should be instructed to flush the eyes with water for 15 minutes and also be urged to see a physician to ascertain whether further treatment is needed. If the product is swallowed, the patient should be taken to an emergency room immediately. 

Calluses

Calluses are another major problem of the feet for which patients seek relief. These are also caused by pressure and friction.1,13 In response to repeated trauma of this type, the stratum corneum produces a thicker keratin layer that is designed to protect the body from future pressure and friction. Calluses occur on the parts of the feet that most need them when we walk, such as the bottoms of the toes, the ball of the foot, and the heel. Calluses do not have a central core like a corn and are a more diffuse thickening. 

Whereas the central core of the corn causes pain and can be removed, the callus is meant to relieve pain, and should not be drastically reduced. If the patient decides to remove all of the calluses on the feet, for instance, he or she will find that walking will be extremely painful until the calluses are allowed to reestablish themselves. In a few cases, calluses may grow to the point where they are uncomfortable, and in those instances they may be carefully reduced. Salicylic acid is also safe and effective for this use. The collodions may be used as described above, or the patient may purchase special, larger-sized plasters such as Dr. Scholl’s Extra-Thick Callus Removers. 

Cushioning Products

Patients may also discover that placing appropriate cushioning/padding products inside the shoe or on the foot can help relieve pain of corns and discomfort of thick calluses.1 Dr. Scholl’s Molefoam and Moleskin Plus Padding are adhesive backed and can be cut to the size needed. Dr. Scholl’s Foam Ease Corn Cushions and Foam Ease Callus Cushions are foam circles that adhere to the corn or callus to protect the foot against shoe pressure. 

Mechanical Removal

Some patients become impatient with salicylic acid and attempt to remove the corn or callus with drastic measures, such as pumice stone abrasion, sanding with files or graterlike contraptions, and slicing them away with “corn planes” containing razor blades.1 These products should be used cautiously and only by a podiatrist or physician. While the devices are sold in pharmacies, it is prudent to recommend against their use.14 Overzealous use can traumatize the skin to the point of inducing infection, skin damage, and bleeding and may lead to severe consequences. 

Conclusion

Patients complain of numerous foot problems in addition to those discussed. When the problem is a serious one, the patient should always be referred to a podiatrist or physician for appropriate medical care. 

Choose Footwear Wisely

One major step to take in caring for the feet and preventing problems is choosing the proper type of footwear. This advice will be one of the hardest aspects to understand and follow in foot care. Many people who want to appear attractive dress their feet in shoes that inevitably cause lifelong problems. For instance, a well-accepted method to look better is to make one’s feet appear dainty. This may take the form of intentionally purchasing shoes that are one or two sizes too small. The foot is forced into an environment where the toes are smashed together and the short heel-to-toe length puts the foot in an abnormal position. Other people purchase shoes that have a drastically tapered tip, also known as a tight toe box. The tight toe box does the same damage as shoes that are too small. Shoes that tilt the feet, such as high heels, are a sure ticket to back and joint problems, damage to the Achilles tendon, and such foot problems as hammer toe, bunions, stress fractures, corns, calluses, and nerve damage. 

Another aspect of choosing footwear is to examine the type of sole before purchase. You should select shoes that provide a nicely padded, soft, resilient sole for you to tread on. Shoes with thin, rigid soles lack the ability to absorb shock, forcing your foot to bear the burden of the forces of walking, running, jogging, or hiking. 

Know a Podiatrist

When you first notice foot discomfort, you may Consult Your Pharmacist, especially for such problems as corns and calluses. However, many more serious foot problems are best dealt with by first making an appointment with a physician or podiatrist. Physicians can help with foot problems; however, the podiatrist is a professional who has chosen to specialize in conditions affecting the foot, just as a dentist specializes in care of the teeth. Shop around for a good podiatrist just as you would when choosing a physician. 

Be Wary of Do-It-Yourself Foot Care

Many misguided individuals think they can self-treat serious foot problems. This can lead to injury and permanent damage. You should always see a podiatrist or physician for care of an ingrown toenail, for instance. Some people try home surgery, using scissors, knives, razors, and other tools to cut out the infected toenail. These interventions often leave a piece of nail embedded in the skin, causing an infection to begin or worsen. Others decide to cut off corns or calluses with razor blades or knives. This is also a bad move, as these individuals are not competent to know when they have penetrated too deeply and perhaps caused an infection. 

The discomfort of corns and calluses can be relieved by placing appropriate cushioning products inside the shoe or on the foot, such as Dr. Scholl’s Foam Ease Corn Cushions. OTC products containing salicylic acid (e.g., topical liquids such as Mosco Liquid Callus & Corn Remover and adhesive-backed plasters or disks such as Dr. Scholl’s Corn Removers) can be applied to safely treat minor corns and calluses. 

Conclusion

Your feet need to stay as healthy as possible to perform their duties. Guard them well and treat them gently, as foot problems can be agonizing and will greatly hamper your ability to carry out the normal activities of daily life. 

Remember, if you have questions, Consult Your Pharmacist. 

REFERENCES

1. Pray WS. Nonprescription Product Therapeutics. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2006.
2. Krul M, van der Wouden JC, Schellevis FG, et al. Musculoskeletal problems in overweight and obese children. Ann Fam Med. 2009;7:352-356.
3. Corns and calluses. Baby your feet. Mayo Clin Health Lett. 2008;26:7.
4. Coles S. Footwear and offloading for patients with diabetes. Nurs Times. 2008;104:40,42-43.
5. Menz HB, Zammit GV, Munteanu SE. Plantar pressures are higher under callused regions of the foot in older people. Clin Exp Dermatol. 2007;32:375-380.
6. Take charge of your diabetes. CDC. www.cdc.gov/diabetes/pubs/tcyd/appendix.htm. Accessed August 27, 2009.
7. Corns and calluses. MedlinePlus Encyclopedia. www.nlm.nih.gov/medlineplus/ency/article/001232.htm. Accessed August 27, 2009.
8. Menz HB, Morris ME, Lord SR. Footwear characteristics and foot problems in older people. Gerontology. 2005;51:346-351.
9. Coughlin MJ, Kennedy MP. Operative repair of fourth and fifth toe corns. Foot Ankle Int. 2003;24:147-157.
10. Herman BE, Corneli HM. A practical approach to warts in the emergency department. Pediatr Emerg Care. 2008;24:246-251.
11. Fluhr JW, Cavallotti C, Berardesca E. Emollients, moisturizers, and keratolytic agents in psoriasis. Clin Dermatol. 2008;26:380-386.
12. Becerro de Bengoa Vallejo R, Losa Iglesias ME, Gomez-Martin B, et al. Application of cantharidin and podophyllotoxin for the treatment of plantar warts. J Am Podiatr Med Assoc. 2008;98:445-450.
13. Rajan M, Pogach L, Tseng CL, et al. Facility-level variations in patient-reported footcare knowledge sufficiency: implications for diabetes performance measurement. Prim Care Diabetes. 2007;1:147-153.
14. Take charge of your diabetes. 9. Foot problems. CDC. www.cdc.gov/diabetes/pubs/tcyd/foot.htm. Accessed August 27, 2009.
15. Dunn JE, Link CL, Felson DT, et al. Prevalence of foot and ankle conditions in a multiethnic community sample of older adults. Am J Epidemiol. 2004;159:491-498. 

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