Could be dermatitis. Dermatitis is an umbrella term that encompasses any skin inflammation or irritation. Some dermatitis is genetic, like eczema. Some is environmental, like poison ivy. While dermatitis is not generally a serious condition, it can cause significant discomfort and is quite unsightly.
Signs of dermatitis include reddened, itchy, raised, swollen, or scabby skin. When these symptoms appear on the feet and have no obvious cause (such as walking through a field of poison ivy barefoot) we have to look at other factors such as shoe contact dermatitis.
Shoe contact dermatitis occurs when the foot produces an allergic reaction to a compound or material used in shoe making. Rubber accelerators and rubber glues are common culprits. For leather shoes, chemicals such as dimethyl fumarate, chromates, and formaldehyde (all commonly used to treat leather products) can provoke an outbreak. Another common cause are specialty dyes and metal decorations containing nickel or cobalt.
Now, I know what you’re going to say, “but Doc, I’ve worn these shoes for years and this has never happened before”. Unfortunately, just blaming it on a new pair of shoes doesn’t quite work. Chromates, used in leather tanning, can slowly leach out of the material and onto the foot due to our feet sweating inside the shoes. Materials can wear thin over time, exposing glues and bonding agents that may have been previously covered. And unfortunately, it is not uncommon to suddenly become allergic to something that you used to be fine around.
Treating shoe contact dermatitis and preventing it from returning are relatively easy. Identify and remove the offending pair of shoes from your wardrobe and avoid contact with those materials again. Allergy skin tests can be helpful in determining what specifically you are allergic to. For future shoe buying purposes, go for materials treated naturally (ever heard of vegetable tanned leather?) and think about replace rubber insoles with foam. To take care of your shoes, control your foot perspiration with powders, creams, or good socks and make sure to air out your shoes regularly.
The only caveat to shoe contact dermatitis is that it’s important to rule out more serious possibilities. Jumping to the allergic reaction conclusion could leave you ignoring the possibility of bacterial or fungal infections, undiagnosed psoriasis, or other causes. If you have any question about what is causing that annoying, inflamed, itchy rash on your feet, make an appointment with your podiatrist to be sure.