What is a boil?

The British Association of Dermatology defines a boil, also known as furuncles, is an infection of the skin which leads to an abscess in the skin. The infection begins from the hair follicles and first extends to the neighbouring skin and, then, the deeper layers of skin.¹ Boils can be as small as a pea and as large as the size of a ball.² Boils are a common universal infection that is painful and can have a negative effect on an individual's well-being.³ Sometimes more than one hair follicle is infected (follicles lying next to each other may get infected) and these combine to form a lump known as carbuncles.⁴Carbuncles are very big swellings with several openings releasing pus that can be extremely painful and upon healing leave a scar. They are usually more serious than furuncles.⁵ Boils may occur once or twice but it may happen again several times in certain individuals and can spread most especially when one has physical contact with an infected person.⁶

What increases the possibility of having a boil?

There are specific factors that can put a person at risk of having boils. These include skin conditions or diseases that disturbs a healthy skin's health. They include:^7,8

• Burns
• Cuts
• Deep Injury or wounds
• Insect stings
• Eczema
• Contact eczema
• Chickenpox
• Pemphigus
• Diabetes 
• Alcohol abuse disorder,
• Malnutrition, 
• Immune deficiencies such as Acquired immune deficiency syndrome (AIDS)
• Obesity
• Poor hygiene 
• Crohn's disease, ulcerative colitis
• Kidney failure
• Fungal skin infections 
• Aged people 
• Poor blood supply
• Living in hot and humid areas

Regions of the body that are prone to boil

Boils are likely to occur in areas of the skin susceptible to sweating, rubbing, obstruction or congestion, like⁵

• The neck
• The face
• The armpit
• The buttocks

Even though boils can be seen in any part of the body with hair, they are seen many times in areas with chunky skin like:^1,6

• The back 
• The back of the neck
• The thighs

 Boils also thrive in parts of the body that are moist like:⁹

• The navel
• The base of the armpit
• The groin
• The intergluteal cleft aka the groove between the buttocks
• Behind the knee
• The inner elbow 

Other parts of the body affected by boil are:^2,10

•  Chest
•  Stomach
•  Arms
•  Lower legs
•  Scalp
• Palm
• soles
• Toe box
• Nasal mucosa i.e the membrane that lines your inner nose

Symptoms of skin abscess - How to recognise a boil

Initially boils may be mistaken for pimples but over the next hours and days the following happens:⁸

• The area of the skin becomes red,hard or palpable (i.e. can be touched or felt because the abscess is on the surface) and swollen. When boils become a carbuncle, the boils form a large, hard lump
• The boil will be painful and warm
• Noticeable buildup of pus( i.e. the whitish or yellowish infectious thick fluid below the skin that contain white blood cells, bacteria and dead skin cells) at the centre

If the infection Is severe it affects the entire body.

Systemic symptoms

 Systemic symptoms include:

• Fever: A fever is an increase in your normal body temperature. Fever is an indication that your body is fighting against an infection. Fever can also occur when there is no infection. Simply put fever is an automatic response to an imbalance in the function of the body caused by an infection.¹¹ Normally the temperature of the human body is around 37 degrees Celsius(°C) or 98.6 degrees Fahrenheit (°F). However, the body temperature can fluctuate by 0.5 °C throughout the day depending on the functional state of the human body. These include¹²
  • Changes in metabolism or metabolic disorders as seen in diabetes
  • Hormonal fluctuation as observed around the menstrual cycle
  • Change in activity levels for example physical exercise
  • sleep/wake cycle

In addition, fever can be classified into grades. They are¹³

It is important to note that the temperature of fever varies slightly depending on the region of the body and the thermometer used.

What goes on in your body when you have a fever? The following happens¹⁴

• The body changes from using glucose to using the by-products of protein and fat. The reason for this is because bacteria thrive on glucose
• The body increasingly uses proteins as a source of energy
• The immune system works harder by increasing the activity and movements of white blood cells, T-cells and interferons
• The growth of certain microbes that trigger infection is stopped due to an increase in body temperature. This occurs because these infection-causing microorganisms do not thrive in increased temperatures

In addition, you will experience the following signs and symptoms¹⁵

• Reddening of the face aka flushing
• Palpitation
• High rate of breathing
• Body pain 
• Very warm and dry skin
• Headaches 
• Lack of appetite
• Feeling constipated or passing loose /watery stools
• Feeling like throwing up
• Throwing up
•  Malaise: malaise means you feel generally unwell and not comfortable
• Fatigue- fatigue is^16,17
• Feeling very tired
• Exhausted
• Experiencing low-energy
• Increased desire to sleep
• Daytime sleepiness
• Constantly feel sad and lose interest or enthusiasm in activities you once loved to engage in
• General body pains
• Feeling very anxious, nervous and easily annoyed
• Enlarged lymph nodes (lymphadenopathy) close to the site of infection. For example if you have a boil in your armpit the lymph node in your armpit will be swollen. Similarly a boil in any part of the legs will result in swollen lymph nodes in the groin. Enlarged lymph node occurs because of your body's immune system i.e. white blood cells are fighting off an infection
• Ulceration (open sore)

In furuncles enlarged lymph nodes and fever not so frequent¹⁸ however, systemic symptoms are more common in individuals with carbuncles.¹⁹

Summary

Boils also known as furuncles is an infection of the skin. The structures of the skin infected are the hair follicles, neighbouring skin and the deeper layers of the skin. The size of boils also varies. When multiple boils join together to form a lump this is known as a carbuncle. Carbuncles are more severe than furuncles. Boils are associated with the following signs and symptoms such as swollen skin that is painful, warm and filled with pus. In severe infection an individual may experience fever, extreme tiredness, malaise, enlarged lymph nodes and so on.