Have you ever wondered why feet sometimes smell unpleasant, particularly after a long day? The answer lies in the complex world of the foot microbiome – an ecosystem of microscopic organisms living on your feet. Here, we will dive into the science behind foot odour and discover how understanding your foot’s bacterial community can help you maintain better foot hygiene.

What Is the Foot Microbiome?

Your feet are home to millions of bacteria, fungi and other microorganisms that make up what scientists call the foot microbiome. This invisible ecosystem plays a crucial role in both foot health and, yes, that distinctive foot odour we’re all familiar with.

The main players (bacteria) responsible for foot odour are:

• Brevibacterium
  Found in French cheeses, this bacterium breaks down dead skin cells to produce methanethiol, creating that characteristic ‘cheesy foot’ odour. It thrives particularly well between the toes.
• Staphylococcus
  Common on feet, these bacteria feed on fatty acids in sweat to produce isovaleric acid, creating a vinegar-like smell. While mostly harmless, some species can cause skin infections if they overgrow.
• Propionibacterium
  These bacteria digest oily substances in sweat, producing propionic acid with its sharp, acidic smell. They flourish in the deeper layers of skin around sweat glands.
• Corynebacterium
  The most prolific odour-producer, Corynebacterium breaks down sweat compounds to create a strong, pungent smell. These bacteria thrive in the warm, moist environment inside shoes.

Why Do Feet Sweat?

The soles of your feet contain eccrine sweat glands at a higher concentration than most other parts of your body – approximately 250,000 per foot. This high density of sweat glands serves several important physiological purposes:

Temperature Regulation
Sweating is your body’s natural cooling mechanism. During physical activity or in warm conditions, these glands produce sweat to help regulate your body temperature through evaporative cooling.

Grip and Protection
A small amount of moisture on your feet actually helps improve grip and protects the skin from friction damage while walking. This was particularly important for our barefoot ancestors.

Emotional Response
Like your palms, your feet may produce sweat in response to emotional triggers such as stress or anxiety. This response is controlled by your sympathetic nervous system.

Medical Considerations
Some people experience excessive foot sweating, known as plantar hyperhidrosis. This condition can significantly increase the likelihood of problematic foot odour and may require medical intervention.

The Perfect Storm: Why Shoes Make It Worse

Modern footwear creates ideal conditions for odour-causing bacteria:

• Enclosed with limited ventilation
• Often manufactured with synthetic materials such a vinyl and polyester
• Warm temperatures
• Moisture retention
• Dark environment

These conditions allow bacteria to multiply rapidly, leading to stronger foot odour.

The Science of Smell

When bacteria break down sweat, they produce several volatile organic compounds including:

• Methanethiol
  This sulphur-containing compound produces a pungent smell reminiscent of rotten cabbage and overcooked Brussels sprouts. It’s the same compound that contributes to morning breath and creates that sharp smell when removing sweaty shoes.
• Propanoic Acid
  More complex than just vinegar-like, this compound produces a sharp, acidic smell similar to salt and vinegar crisps mixed with sour milk. It’s a common contributor to general body odour.
• Isovaleric Acid
  This compound creates the unmistakable smell of strong blue cheese. It’s particularly noticeable in feet that have been confined in shoes all day and is also responsible for the pungent aroma of sweaty gym clothes.
• Hexanoic Acid
  While often called ‘goat-like’, this compound has a distinctive waxy, barnyard smell with subtle sweet notes. It’s the same compound found in goat cheese and becomes more noticeable when feet sweat in synthetic materials.

When to Seek Professional Help

It’s important to understand that the presence of bacteria on your feet is completely normal and necessary for healthy foot function. Just like your gut microbiome, your foot microbiome requires a delicate balance of different bacterial species. However, when this balance is disrupted, problems can arise.

Normal vs Problematic Bacterial Balance
A healthy foot microbiome contains a diverse mix of bacterial species in the right proportions. Occasional mild foot odour is normal, particularly after exercise or during hot weather. However, when the bacterial balance is disturbed, certain species can overgrow, leading to persistent and excessive foot odour.

Signs Your Foot Microbiome Might Be Imbalanced:

• Sudden increase in foot odour intensity
• Change in the type of smell
• Persistent odour that doesn’t improve with regular hygiene
• Odour accompanied by skin changes or discomfort

Other Reasons to Seek Professional Help:

• Hyperhidrosis (excessive sweating)
• Fungal infections
• Bacterial infections
• Other underlying health conditions

A podiatrist can help determine whether your foot odour is due to a microbiome imbalance or other factors and recommend appropriate treatments to restore healthy bacterial balance

Top Tips 5 tips for Reducing Foot Odour

1. Keep feet and shoes dry
2. Rotate shoes daily to give them a chance to dry out
3. Wash feet in the shower daily with soap-free wash and use mechanical agitation (soft brush) to remove bacteria
4. Avoid occlusive footwear with limited airflow
5. Choose natural fibre socks high in cotton, wool or bamboo content