Introduction

What is skin cancer?

Skin cancer is the most commonly occurring cancer worldwide.¹ It refers to the abnormal growth of skin cells in the sun-exposed surfaces. It can also be seen less commonly in areas not exposed to sunlight. 

Types

There are several types of skin cancer. The 3 major types are:

• Basal cell carcinoma: The most common type but harmless
• Squamous cell carcinoma: The second most common type; also called epidermoid carcinoma
• Melanoma: The most dangerous type of skin cancer involving abnormal cell growth in melanin-producing cells called melanocytes
  

A healthy weight for a healthy life

A healthy adult's weight is measured by a Body Mass Index (BMI), lying between 18.5 and 24.9. BMI is a measure of body fat, calculated based on a person's height and weight. A person with a BMI of 25-30 is considered overweight. If it exceeds 30, the person is considered obese. According to the World Health Organization (WHO), being overweight is a condition of excessive fat deposits, whereas obesity is a chronic disease (recognised in the late 1940s)of excess fat deposition that can impair health.² 

Overweight and obesity pose various health issues. Alongside the risk of high blood pressure, diabetes, and heart disease, a person is also at risk of cancer. Obesity has been associated with the following types of cancer:³

• Colorectal cancer
• Oesophageal cancer
• Stomach cancer
• Gallbladder cancer
• Liver cancer
• Kidney cancer
• Postmenopausal breast cancer 
• Endometrial cancer
• Thyroid cancer
• Non-Hodgkin lymphoma
• Multiple myeloma
• Skin cancer (see below)

Understanding skin cancer

Types of skin cancer

Basal cell carcinoma (BCC)

• It is the most common type of skin cancer and is rarely fatal⁴ 
• It arises in the basal layer of the skin
• Clinically, it appears as a pink-coloured pearly papule that may be as small as 1-3 mm
• The most common sites involved are the nose and surrounding region, cheeks, and forehead
• It is a slow-growing tumour presenting with crusting and bleeding
• It can be removed surgically to prevent the risk of recurrence⁴

Squamous cell carcinoma (SCC)

• It is the second most common type of skin cancer⁵ 
• It is more common in people assigned male at birth (AMAB), elderly, and fair-skinned (lack of melanin) people
• It may appear as a scaly, red papule, or a deep ulcerated lesion
• It is a malignant form of cancer, which means it can invade nearby tissues and spread to other parts of the body
• The most preferred method of treatment is surgical removal

Melanoma

• Malignant melanoma or cutaneous melanoma is the most dangerous type of cancer arising in melanin-producing cells called melanocytes 
• The number of melanoma cases among white people has increased by 3-6% in the last few decades, making melanoma one of the fastest-growing cancers globally⁶ 
• It can be smaller or larger than a pea in size, with shades of black, brown, or grey
• Melanoma tends to invade nearby tissues and spread to other parts of the body (metastasis)
• It is difficult to treat and has low cure and survival rates after surgery or radiotherapy⁶

Risk factors for skin cancer

Environmental

• Ultraviolet (UV) rays exposure: Sun exposure is the main source of UV radiation. About 60% of melanoma cases in Canada and Australia can be linked to UV rays⁷
• Sunburns: Sunburn refers to the reddening or blistering of untanned skin overexposed to UV rays. It is proven to be a significant risk factor for melanoma⁷
• Tanning beds: A tanning bed is a common concept in western European countries to tan skin. It is a machine that emits UV rays. Its use has been associated with a 20% increased risk of melanoma⁷

Genetic predisposition

Apart from external factors, genetic susceptibility plays a huge role in the development of skin cancer. The risk of melanoma nearly doubles in people with first-degree relatives with melanoma and increases with the number of affected family members.⁷ 

People carrying the faulty MC1R gene have an increased risk of BCC. Other genes with mutations (changes in DNA) include PTCH1 and PTCH2.⁷ Similarly, many genes such as ATM, DSTYK, GPR98, and SOX6 are found to have a high genetic correlation with melanoma, BCC, SCC, and other skin conditions.⁷ 

Lifestyle factors 

• Diet: Studies show including antioxidants such as vitamin C, vitamin E, carotenoids, and selenium in your diet can reduce the risk of skin cancer (discussed later)⁸ 
• Smoking: People who smoke are at an increased risk of SCC. However, smoking is not associated with BCC or melanoma⁹

Symptoms of skin cancer

It’s common to experience skin redness, blisters, moles, bumps, and patches every once in a while. But you must seek professional advice if you notice any of the following symptoms:

• Sudden development of new moles or spots on the skin
• Changes in existing moles
• Uneven, asymmetric moles
• Non-healing ulcers or sores
• Crusting and bleeding of the lesion
• Sudden increase in the size of the lesion
• Rough in texture
• Pink/red in colour 
• Painful and itchy
• Pearly white or wart-like in appearance

Weight as a factor in skin cancer risk

Obesity and skin cancer

Several studies show an association between obesity and an increased risk of skin cancers – particularly melanoma. Obesity often worsens the outcome of melanoma, exhibiting aggressiveness.¹⁰ Another study showed that people who underwent weight-loss surgery showed a lower risk of melanoma and other skin cancers.¹¹

Possible mechanisms

The possible mechanisms behind the link of obesity to skin cancer can be: 

Inflammation caused by excess adipose tissue

Fat cells sustained over a long period release various inflammatory substances such as adipokines. An excess adipose (fat) tissue causes dysregulation of adipokines, leading to chronic inflammation.¹³ This negatively affects the functioning of the organs.¹² 

Release of leptin

Fat cells release a hormone called leptin, which promotes melanoma growth and metastasis by increasing the multiplication of melanoma cells. 

Hormonal changes

Melanoma cells have certain proteins called growth factor receptors on their surface. These receptors include those for insulin and insulin-like growth factor-1 (IGF-1), two key growth factors increased in obese people. They help melanoma cells grow, survive and spread to other areas.¹⁰

Impact on the immune system and ability to repair UV-induced DNA damage

Overexposure to UV radiation, particularly UVB, may suppress the immune system. It damages DNA, blocks the signals to immune cells, and releases substances (cytokines) that slow down the functioning of the immune system.¹⁴ 

Obesity causes inflammation and oxidative stress. Oxidative stress refers to an imbalance between free radicals and antioxidants in the body, which may damage DNA, tissues, and organs. It also inhibits the repair of damaged DNA.¹⁵

Underweight individuals and skin cancer

No conclusive evidence establishes an association between underweight individuals and skin cancers. However, certain factors such as poor body nutrition, weakened immune system, less fat protection, and thin skin increase the vulnerability to skin cancer. More studies and research are required to clarify the relationship between being underweight and skin cancer. 

Lifestyle and skin cancer prevention

Skin cancer is a painful condition but the good news is it is preventable.⁷ With appropriate measures and awareness, you can lower the risk of developing cancer. Here are the steps you can follow to reduce the risk:

Weight management for cancer prevention

Healthy diet 

A healthy diet rich in antioxidants and vitamins can help reduce oxidative stress and free radical formation, which are notorious for skin damage. Major antioxidants are vitamins A, C, and E. Here’s a list of food items rich in these antioxidants:¹⁶

• Beverages: Double espresso coffee, red wine, black tea, green tea, pomegranate and grape juice
• Grain products: Buckwheat, millet, barley flour, crisp bread, wholemeal bread with fibre, walnuts, pecans and chestnuts with pellicle
• Chocolate: Dark chocolate and chocolate products with a higher cocoa content
• Egg yolks
• Berries: Dried amla (Indian gooseberry), wild dried dog rose, fresh crowberries, bilberries, black currants, wild strawberries, blackberries, goji berries, sea buckthorn and cranberries
• Fruits and vegetables: Yellow pith of Spanish pomegranate, dried apples, flour made of okra, artichokes, lemon skin, dried plums, dried apricots, curly kale, red and green chilli and prunes
• Spices and herbs: Dried and ground clove, peppermint, allspice, cinnamon, oregano, thyme, sage, rosemary, and saffron

Physical activity

Regular physical activity is crucial for weight maintenance. Moderate-intensity workouts combined with a healthy diet can help you lose weight significantly. 

Read more here: Eating & Physical Activity to Lose or Maintain Weight

Sun protection practices

• Use sunscreen with SPF 30 or higher for people older than 6 months¹⁷
• Wear protective clothing, hats, and sunglasses whenever you step out
• Avoid peak UV hours between 10 am to 4 pm even on a cloudy day or in the winter season, especially at high altitude

Healthy skincare routine

• Hydrate well and moisturise your skin always. Cover neck, arms and legs as well 
• Consult a dermatologist to know the best skincare products based on your skin type and texture
• Avoid tanning beds and excessive UV exposure
• Observe and self-examine recently developed moles and lesions on the skin
• Seek professional dermatology screening if you notice a non-healing lesion or have priorly experienced skin cancer 

Healthy lifestyle

Alcohol and smoking are the root cause of innumerable health conditions. It is best to avoid smoking at all and consume little to no alcohol for a better quality of life. 

Insights from recent research

Studies on the association between skin cancer and weight are limited. While some studies have established a direct relationship between the two, other studies showed contradictory findings on the “obesity paradox” which means obesity is associated with better outcomes in certain cancers like skin cancer. 

Obese people are less exposed to the sun due to less physical activity such as walking or running outside the home.¹⁸ Another study states obesity is inversely associated with skin cancer.¹⁹ Hence, more research and studies are required to attain an accurate association between weight and skin cancer. 

Summary

Skin cancer is an abnormal growth of skin cells. Three major types of skin cancer are basal cell carcinoma, squamous cell carcinoma and melanoma. They arise due to exposure to UV radiation via sunlight, genetic predisposition, and unhealthy lifestyle practices such as smoking and alcohol consumption. It may start as a small non-healing ulcer and progress deep into the skin invading nearby and distant tissues and organs. Obesity can cause inflammation, hormonal imbalance, and low immunity. This increases the risk of skin cancer. On the other hand, thin skin and fat layers in underweight people may increase their susceptibility to skin cancer. 

Fortunately, skin cancer is preventable. Using sunscreen with SPF 30 or more and wearing protective clothing are the best practices to reduce the risk of skin cancer. Maintaining a healthy weight through lifestyle changes such as moderate-intensity physical activity and a healthy diet can further help in reducing the risk. With more extensive research and studies, we can raise awareness and educate the community about skin cancer risks and weight management.