As we all know, the sun can make us bronzed and beautiful.  Most of us are aware that without sun protection it can also cause skin damage, ageing and cancer.  But what is behind this?  Here comes the science...

UVA and UVB

According to our resident skin care expert, ultra-violet (UV) radiation is composed of UVA and UVB and UVC.  UVC is blocked by the earths atmosphere so none reaches us. 

UVB (UV-Burning) penetrates in to the upper layers of the epidermis and causes sun burn. It can also lead to the development of skin cancer. UVB is more intense in summer months, and summer accounts for 70% of our annual UVB dose.

UVA (UV-Ageing) penetrates deeper in to the skin than UVB and causes tanning and wrinking of the skin.  High doses of UVA such as those found in sun beds can also cause burning and recent research shows it can also increase your risk of developing skin cancer.

Sun Protection Factor

Sun protection factor, or SPF, tells you how long a sunscreen will protect you from burning by UVB radiation.  If your skin burns in 10 minutes without sun cream, then a SPF 6 sun cream will protect you from burning for 6 times 10 minutes, so 60 minutes or 1 hour. 

UV Filters

The active ingredient in a sun cream is the UV filter, there are two main types of UV filters:

• Chemical UV filters - these just absorb UV. Examples are Butylmethoxydibenzoyl Methane, Ethylhexyl Methoxycinnamate, Octocrylene and PABA.

• Inorganic UV filters (also known as mineral or physical UV filters) - these absorb, scatter and reflect UV.  There are only two types of mineral UV filters, zinc oxide and titanium dioxide. These types are often considered to be the most natural UV filters as they are not synthetic chemicals. Unlike chemical UV filters zinc oxide and titanium dioxide exist as particles so do not interact with or penetrate the skin barrier.

Skin Ageing

Up to 90% of the signs of premature ageing (fine lines, wrinkles and age spots) are caused by UV exposure.  UVA penetrates into the epidermis and dermis of the skin where it directly damages collagen and elastin fibres (the structures that give the skin its firmness and smoothness).  UVA also causes indirect damage via the creation of free radicals.  The image above demonstrates the effects of UV ageing, with UV exposed skin on the left, unexposed on the right.

What is a free radical and why is it damaging?

UVA radiation is one of major creators of free radicals.  Free radicals are reactive molecules (normally oxygen) that only have one electron instead of two.  Because electrons have to exist as pairs these reactive molecules must scavenge for, find and react with another electron to create a pair and become stable. This process can damage cellular function and genetic material.  Free radicals cause wrinkles by damaging collagen, and are thought to cause cancer by changing the genetic material (DNA) of the cell.

Radiation Types and Skin Cancer

Scientists now believe that both UVA and UVB rays contribute to skin damage, including skin cancer.

UVB radiation has been proven to cause damage to the DNA of skin cells. Skin cancers develop when this damage affects the DNA of genes that control growth and division of skin cells. Recent research has found that UVA also contributes to skin cancer formation.

The Science of Sun Burn

An obvious side effect of prolonged exposure to the sun is sun burn.  Sun burn usually develops 2-6 hours after sun exposure and it generally peaks after 24 hours.  But with sun burn you can get other symptoms aside form the obvious reddening (or erythema) of the skin.  Skin can be hot to the touch and the person can feel dizzy and generally tired. In severe cases you can experience fever, chills, nausea and delirium. 

Sunburnt skin usually ends up peeling.  Peeling occurs when cells become so damaged that the immune system triggers apoptosis (cell suicide) as a way to prevent cells becoming cancerous.   But there are certain factors (such as UV exposure) that cause this process to fail, cells continue to divide and can become cancerous. 

The pain from sun burn is usually at its worse 1-2 days after the exposure, but peeling and itching can occur for up to 2 weeks.