Archive for the ‘Skin’ Category

Research update

June 2, 2011

Science is ever moving and ever changing, and we’re always finding new things. In this article I’m revisiting some of my past topics with some recent research.

The structure of skin
One of my first articles on thatscienceguy discussed the structure of human skin and how the sun’s radiation affects it. Skin is the largest organ in the human body, and has a critical role in protecting our body from external threats and stopping excessive water loss. The outermost layer, called the stratum corneum, can actually act like a sponge and absorb quite large amounts of water depending on the humidity of the surrounding environment. This ability to absorb water means it needs to be quite flexible, however it needs to balance this flexibility with being robust enough to be able to protect the deeper layers of skin and organs underneath.

Researchers from the Australian National University examined the structure of the stratum corneum to try to understand how its structure allows these dual roles. They found that the keratin filaments which provide skin its structure have a remarkable three-dimensional weave which allows individual fibres to wind and unwind. While the fibres can individually wind and unwind, they do so cooperatively to allow the stratum corneum to breathe without losing structural strength.

The weaving of keratin in its condensed form. From Evans M.E. and Hyde S.T. 2011

The weaving of keratin in its expanded form. From Evans M.E. and Hyde S.T. 2011

Male motor skills
The study which I rated as the strangest of last year investigated the perfect male dance moves to attract women – they even produced videos which demonstrated these moves. Needless to say, it was quite a popular topic!

I explained the importance of that study by likening it to courtship displays by other animals – the males will put on a ‘show’ to demonstrate their prowess to the female, and in the case of humans, dancing may well be one of our courtship displays. But the question remained why exactly do animals (including humans) put on these courtship displays, what exactly are they exhibiting?

Studying the manakin bird, researchers from the University of California Los Angeles found that the female birds preferred to mate with males who performed the courtship display at greater speeds, and were able to tell differences measured in the milliseconds. The speed and energy exertion required by the male to do this courtship display means they have extremely fast heart rates. From this the authors suggested that the courtship display is actually a demonstration of the male’s motor skills, coordination and cardiovascular qualities, and so being able to do it faster shows that the male is stronger and has better quality genes.

And for those wondering what the manakin bird is, from QI:

Sexual attraction
Back at the start of April I blogged about the science of sexual attraction, and in the intervening two months new research has been released which is worth examining.

In the original articles I wrote about the effects testosterone has on males and their attraction to women, and attractiveness to women. Now, new research has shown that men who have higher testosterone are flirtier. Remembering back, testosterone is important for competition between males, so researchers increased men’s testosterone levels by making them compete in computer tasks. The men who showed the highest increases in testosterone as a result of the competition subsequently showed more interest in the woman, made more eye contact with her, smiled more and talked more about themselves. So the testosterone increases induced by competition makes men more attentive to women – maybe this means the best plan before a big date is to do something competitive.

Males have also been found to be able to distinguish whether a female is fertile just from looking at her face. Back in the original articles I wrote how oestrogen levels, which rise during ovulation, slightly change the shape of a woman’s face, making it more rounded and considered as slightly more attractive. Using macaques (a species of monkey), new research has shown that men can recognise these signs of a female’s fertility, but only in faces they are familiar with. Researchers showed male macaques images of females faces which had been classified as being pre-ovulation, during ovulation, or post-ovulation (they found these stages out from measuring the female’s hormones). The male macaques were able to tell the difference between the faces of during ovulation and pre-ovulation, however they could only tell the difference if they were familiar with the particular female. When showed images of an unfamiliar female, they couldn’t tell the difference.

Little is known about the molecular reasons for sexual preference, but research published recently in Nature has investigated how chemicals in the brain may affect who we find attractive. Serotonin, also known as 5-HT, is known to have a huge effect on mood – in fact the most common drug treatment for depression works by making serotonin last longer in the brain. The researchers found that male mice normally prefer female over males as mates. However, when the same breed of mice was modified to make them unable to produce 5-HT, the males lost their sexual preference. When these mice had their 5-HT production restored to normal levels they regained their preference of females over males. This research is the first to show that 5-HT may be involved in sexual preference, and raises the question of whether other brain chemicals are involved in sexual preference.

Lapping dogs
And finally, another update from the strangest research studies from last year, this time the study which examined how cats drank. They found then that cats used the back of their tongues, skim over the surface of the liquid, and then pull rapidly upwards into their mouth. The surface tension would lift the liquid with their tongue straight into their mouth. This seemed much more refined than the simple scooping method that dogs use.

But do dogs really just scoop liquid? It turns out that comment was premature, as new research has now found. Using high speed video it has now been found that dogs too use a very similar method as cats, picking up liquid with the back of their tongue and relying on surface tension and inertia to keep the liquid in place. The liquid travels with the tongue through the oral cavity into the oesophagus, with the tongue then pressing up against the roof of the mouth to prevent the liquid from falling out.

You can see it all in action in these videos:

This is a 300 fps video of a dog lapping. It seems to show spooning of liquid into the mouth but X-ray video tells a different story. From Crompton A.W. and Musinsky C. 2011

This video shows that, contrary to published accounts, dogs do not scoop liquids into their mouths with a spoon-shaped cavity that forms in the ventral surface of a backwardly directed tongue tip. As in cats, an aliquot of liquid adheres to the dorsal surface of the tongue tip and is transported into the oral cavity as the tongue is rapidly withdrawn. From Crompton A.W. and Musinsky C. 2011

What does the sun actually do to your skin? Part 2

February 6, 2011

In part 2 of this series about the effect of UV on skin, we look at skin cancer and the most effective ways to protect yourself from the damaging effects of the sun.


Skin cancer

Skin cancer is the most common cancer in the western world, in Australia it affects four times as many people as every other type of cancer combined. In fact Australia has the highest rate of skin cancers of anywhere in the world and it has been estimated that between 60-70% of the population will have skin cancer at some point in their life. The major cause of skin cancer is UV radiation, and despite the success of campaigns such as “slip slop slap”, this rate is increasing.

There are 3 main types of skin cancer, basal cell carcinoma (BCC), squamous cell carcinoma (SCC) and malignant melanoma.


From left: Basal cell carcinoma, Squamous cell carcinoma, Malignant melanoma. Images courtesy of the Australasian College of Dermatologists

The first two types, BCC and SCC are tumours which are originally keratinocytes which have become sun damaged and now rapidly grow and divide, with BCC forming from keratinocytes deep in the epidermis, while SCC form from keratinocytes closer to the surface. Malignant melanoma however, is originally a sun damaged melanocyte. The BCC and SCC types make up most skin cancers, together around 96%, with melanoma making up most of the remaining 4%. Despite only being a small fraction of skin cancers, melanoma is responsible for around three-quarters of skin cancer deaths in Australia, a result of its fast growth and ability to spread rapidly through the body.

Keratinocytes and melanocytes both become cancerous from damage caused by UV radiation. In fact, the amount of UV radiation needed to cause damage leading to skin cancer is far less than that needed to cause a sunburn. UV penetrates the cell and damages DNA, which is effectively the instructions for how the cell works. This damage can sometimes be repaired by the cell, however if these repair mechanisms don’t succeed, the damage may be permanent. There are several genes (sections of DNA) in particular which when damaged have a high probability of causing cancerous growth. One gene, called Braf is found to be damaged in between 50% and 80% of melanoma cells, and causes increased growth rates of cancerous cells. Other genes which normally hinder cell growth are also often found to be damaged in skin cancer cells, as are genes which normally cause cancer cells to die. Genes which are involved in DNA repair are also sometimes found to be damaged in cancer cells, as damage in these areas means the cell may not be able to repair other DNA damage properly. These changes to the DNA caused by UV radiation result in cells which have fast, unlimited growth which then form tumours.


DNA damage by UV radiation


UV also causes changes to the cell processes which regulate its growth. When exposed to UV radiation, skin cells can increase the production of chemicals which increase the speed of cellular growth, not only of the cell producing the chemical, but also of cells around it. UV also causes the increased production of chemicals which cause inflammation, and these can also cause damage to the cell and also act to increase its growth.

While melanin does provide some protection to the skin cells from the effects of UV, even if you’re someone who tans darkly it is still vitally important to properly protect your skin. A dark tan on white skin only provides a protection of around SPF 4, compared to most sunscreens which provide protection of around SPF 30. Also, remembering the structure of skin, for UV radiation to reach and activate the melanocytes means it has to travel through all the layers of epidermis, potentially damaging the keratinocyte cells on the way. The tan is effectively a way of the body trying to protect itself against more damage. So while having a tan will partially protect you, your skin cells have potentially been damaged to get the tan in the first place. This is why many sun experts use the saying “There’s no such thing as a safe tan”, because you may have received cancer-causing damage to get that tan.

Ultraviolet light also causes a reduction in the effectiveness of your immune system. Normally, the immune system has a role in preventing cancer by identifying and then removing cancerous cells from the body. However, when suppressed by UV radiation, the immune system isn’t as effective in removing cancer cells, allowing them to remain and form tumours.



It is important when using sunscreens not to think of them as blocking UV. They are in fact only a filter which reduces the amount of UV which reaches your skin by forming a barrier to UV radiation. The strength of this filtering out of UV is shown by their SPF rating. The SPF number is a ratio of the time or dose of UV required for sunburn of protected skin to the time or dose of UV required for sunburn of unprotected skin. For example a sunscreen with an SPF of 20 means that skin protected by the sunscreen will take 20 times longer to burn compared to skin without sunscreen. Another way of thinking about it is that it is an indication of how much UV is allowed to penetrate your skin. For example, in Australia, the highest SPF rating allowed to be shown on sunscreens is 30+, which means it limits the UV reaching your skin to one-thirtieth of the levels than if you hadn’t been wearing the sunscreen.


An SPF30+ broadspectrum sunscreen. Image courtesy of the Cancer Council Australia


Internationally, there are products sold which claim to be tanning sunscreens. The way these products work is by only blocking some UV radiation, allowing the remaining UV radiation to pass through. UV radiation which reaches the earth’s surface is classified as two types, UVA and UVB. These tanning products work by filtering out UVB but allowing UVA to pass through the skin to activate the melanocytes. The problems with these products are many. Firstly, they sometimes only have a very low SPF factor (I’ve seen one with an SPF of 2), meaning they give poor sun protection to begin with. Secondly, UVA radiation is the type which causes nearly all of the damage to the skin structure, meaning you have no protection against the premature aging effects of UV. UVA is also responsible for the production of chemicals in the skin called “free oxygen radicals”. These chemicals can cause significant damage to cells, damage which can lead to the onset of skin cancer. UVA also causes the reduced immune system activity that helps skin cancer cells stay alive. Finally, UVA is a strong promoter of cancer growth, meaning that if there are any damaged cells in your skin it will make them grow very quickly, and this effect is particularly seen with melanoma. So while you may think you’re using a sunscreen and will be protected against the bad effects of UV, in practice there is effectively no protection given by tanning sunscreens.

When using a sunscreen it is absolutely vital to use broad-spectrum sunscreens, which filter both UVA and UVB at an equal level, giving the maximum amount of protection against all of the damaging effects of UV.


Next time you’re in the sun, just remember what the effect it’s having on your skin. The most effective way of avoiding skin cancer is still by being sunsmart – that is, slip on a shirt, slop on broad spectrum sunscreen and slap on a hat, and avoiding the sun by seeking shade as much as possible between 11am and 3pm. By staying smart in the sun you will be able to reduce the harmful effects of sun exposure, not eliminate, but reduce as much as practically possible, while still getting the beneficial effects of the sun.


A great resource for skin cancer information is the Cancer Council Australia website

What does the sun actually do to your skin? Part 1.

January 28, 2011

This is part 1 of thatscienceguy’s articles about the effects that the sun has on your skin. This week we look at skin itself, the damage the sun does to the structure of your skin and the health benefits of sun exposure.

In Australia we’re encountering another typically sunny summer, and it’s extremely important to properly protect ourselves from the harmful effects of the sun. This makes it the perfect time to examine just what the sun does to your skin and why it’s important to protect ourselves.

Before we can talk about the effects that the sun has on skin, let’s first look at skin itself. Skin is the largest organ of the human body and its main job is to provide protection for the bones, tissues and internal organs and prevent too much water being lost from the body. It is made up of two main areas, the surface epidermis and the deeper dermis layer.

Cross section of human skin (Adapted from Stulberg et al)

The epidermis is the topmost layer, and is made up mainly of cells called keratinocytes. Keratinocytes begin in the deepest layer of the epidermis and are pushed upwards by the production of more cells beneath them. By the time they reach the surface they have died, and it is these layers of dead cells which provide protection and waterproofing to the layers underneath.

The dermis makes up most of the skin and acts as a base for the epidermis. As it acts as a base, the dermis is rich in a substance called collagen, which provides strength and resistance to damage. As well as collagen, the dermis is also rich in elastin fibres, which as the name suggests allows skin to stretch and recoil. Hair follicles and sweat glands are also found in the dermis.

Ultraviolet (UV) light from the sun has many effects on the skin. Australia receives some of the highest levels of UV of anywhere in the world – the UV levels during winter in Australia are equal to the UV levels during summer in The Netherlands. The map below shows the UV levels in Australia during a typical summer day, with every populated location on mainland Australia in the “extreme” level of UV radiation.

Map of summertime UV levels in Australia. Purple areas represent extreme UV levels. (Image courtesy of the Australian Bureau of Meteorology)

In between the epidermis and dermis are cells called melanocytes which, when exposed to ultraviolet radiation from the sun, produce a dark substance called melanin. Melanin is absorbed by the keratinocytes, which then use it to protect themselves from UV as a kind of sunshade. This melanin response to UV has evolved as a natural sunscreen, providing protection to the keratinocyte cells by absorbing incoming ultraviolet radiation and produces the visible tanning effect. People who tan darkly from sun exposure have a lesser risk of skin cancer because of the protection given by melanin.

In addition to the tanning effect, UV light also attacks the elastin and collagen of the skin, damaging collagen and causing tangling of elastin. This damage results in the loss of skin’s structure, which is what causes sagging, wrinkling and increased roughness of sun-damaged skin. UV also increases the production of free oxygen radicals, small molecules which attack and damage the skin cells. These effects are permanent and lead to noticeable premature aging.

Vitamin D

As well as protecting your body, skin also has a vital role in the production of a chemical in your body called vitamin D. Up to 90% of vitamin D is produced by the skin by a mechanism which actually requires UV radiation. Vitamin D is beneficial to health, and in fact the World Health Organisation recommends UV exposure to reduce diseases such as bone defects including osteoporosis and rickets, diabetes, some cancers and heart disease.

Because the production of vitamin D requires UV, theoretically there is the chance that using sunscreens or avoiding sun exposure may lead to vitamin D deficiency. However, this very rarely happens as the amount of  sun exposure needed to make enough Vitamin D is extremely small. Only a couple of minutes of exposure to the sun are enough to produce sufficient vitamin D, so just normal day-to-day exposure when people don’t normally wear sunscreen is satisfactory. Also, when applying sunscreen it is normal that people will accidentally miss a small area, or cover some areas lighter than others. The exposure to UV from these areas is also often sufficient for the production of vitamin D. While there may be rare cases of people not getting enough vitamin D, it is incredibly unlikely to happen due to using sunscreen or by being sunsmart and people should not be concerned, nor should they seek out sun specifically for the reasons of vitamin D production.

The ozone layer

Just a final note about the importance of the ozone layer. UV light is separated into 3 types, UVA, UVB and UVC, although effectively all UVC and most UVB is absorbed by the ozone layer. This means that around 90-99% of UV radiation reaching the surface of the earth is UVA, with the remaining 1-10% being UVB. Although the ozone layer does filter out a lot of UV radiation, it has been calculated that a 1% decrease in ozone actually results in a 2% increase of UV dose, so the integrity of the ozone layer is vital for human health.

The hole in the ozone layer over Antarctica. Purple and blue areas are regions of very low levels of ozone (Image courtesy of NOAA)

Over the last decade the breakdown of the ozone layer has been slowing due to the ban of CFC-containing aerosols. CFC’s contain chlorine which is very reactive in breaking down ozone, and human activities are responsible for around 75-85% of the chlorine in the atmosphere. Estimates suggest however that chlorine levels in the atmosphere may be peaking at the moment, and as levels begin to drop the ozone hole may begin to close. However, this is a slow process and it will be at least a decade before any measurable changes to the size of the ozone layer can be seen.

Part 2 will be published next week looking at skin cancer and the importance of sunscreens.