Happy Summer Solstice - Now Don't Get Burned...

Do you remember that bad sunburn you once got? How painful it was? How red your skin looked and felt like? Well, your skin does remember too! For the rest of your life...

Severe sunburn on the shoulder of a 30 year old woman. The skin has become reddened, inflamed and blistered due to overexposure to the ultraviolet light in sunlight. Burns causing blistering are classified as second degree burns.

As we officially start summer on June 20, 2012 and we get to experience the longest day (by that I mean daylight hours), it is a good idea to quickly review the issue of sun-overexposure. But first, why does summer start on the longest day of the year? Shouldn't we already be halfway through the summer?

Blame the oceans, which heat up and cool down only slowly. By June 20 they are still cool from the winter time, and that delays the peak heat by about a month and a half. Similarly, in December the water still holds warmth from the summer, and the coldest days are still (on the average--not always! ) a month and a half ahead.

Every planet in our solar system has seasons. But the seasons that occur on other planets are extremely different from the traditional spring, summer, fall and winter that we experience here on Earth. Despite what may seem like great variations in temperature, weather and climactic conditions in different places around the globe, in reality, there actually is little variation in Earth's overall climate. Why?

There are two reasons that seasons occur on the planets: the tilt of a planet's axis and its orbit around the Sun. Our orbit is nearly circular, so there is little variation in Earth's overall climate. But, other planets have more elliptical - egg-shaped - orbits, and therefore their seasons are very different than what we experience. The terms "summer" and "winter" tend to be Earth-oriented terms, but can be applied to the other planets as well. When the North Pole of any planet is tilted toward the Sun, astronomers call it the Winter Solstice; when the South Pole is tilted toward the Sun it's called the Summer Solstice.

Now with Summer starting in the Northern hemisphere, it is a great time to warn you again of those nasty sunburns...

Sunburns

If you have been inside all winter and then go sit out in the sun on a bright spring day, it is very easy to get sunburned. Over the course of several hours, exposed skin turns bright red and becomes extremely painful when touched. The skin will often feel very warm as well.

When you get a sunburn, you're basically killing skin cells.

The Skin 

Skin is one of the most amazing organs in the human body. It is hard for us to think about it as an organ, however. We tend to think of organs as boxy things. Your heart, liver, kidneys - those are obviously organs. But skin is an organ too, especially if you look at the dictionary definition of "organ", like this definition from the Merriam Webster Collegiate Dictionary:

Organ - 

a) differentiated structure (as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism 

b) bodily parts performing a function or cooperating in an activity

By that definition, skin is definitely an organ. Skin is made up of very specific cells and tissues, and their collective purpose is to act as the boundary between "you" and "the world". One of the neat things about skin that makes it different from a lot of other organs is the fact that it does have to deal with the real world. Therefore it is loaded with sensors, and it also has a very tough layered design so that it can handle realities of the environment like abrasion and sunlight.

The living, inner layer of the skin is called the malpighian layer. The malpighian layer creates the dead cells that we can see. It is in direct contact with the dermis, which feeds and supports it. The malpighian layer is our focus of attention actually, because it is here that the sun affects the skin during tanning. The malpighian layer is itself layered like this:

- In direct contact with the dermis is the basal layer. If you have ever heard of a basal cell carcinoma (cancer), this is where it starts.

- Above the basal layer is the spinous layer.

- Above the spinous layer is the granular layer.

- Above the granular layer is the stratum corneum. The stratum corneum is the outer layer of dead cells -- the cells that we see as our skin. The cells in this layer are filled with a protein called keratin. Keratin is a very interesting protein because it is tough -- horns, hair, hoofs, fingernails and feathers all gain their strength from keratin. The same stuff that your fingernails are made of actually forms your visible skin (but in a much thinner and more flexible layer). That is what makes your skin so tough. In parts of the body that get a lot of wear, like the palms and the feet, the stratum corneum is thicker to handle the abrasion.

Living among the basal cells in the malpighian layer is another type of cell called a melanocyte. Melanocytes produce melanin, which is a pigment that is the source of tanning. The melanocytes are actually where a tan comes from. 

Not only do melanocytes produce a tan, they are also responsible for the form of cancer called melanoma. Melanoma is caused by UV radiation damage to melanocytes. Repeated exposure to UV can cause cancerous mutations.

Sun Taning vs Burning
So, now that we know all about the skin we can start to actually understand tans and sunburns. When you get a tan, what is actually happening is that the melanocytes are producing melanin pigment in reaction to ultraviolet light in sunlight. Ultraviolet light stimulates melanin production. The pigment has the effect of absorbing the UV radiation in sunlight, so it protects the cells from UV damage. Melanin production takes a fair amount of time -- that is why most people cannot get a tan in one day. You have to expose yourself to UV light for a short period of time to activate the melanocytes. They produce melanin over the course of hours. By repeating this process over 5 to 7 days pigment builds up in your cells to a level that is protective.

The previous paragraph applies to Caucasians. In a variety of other races, melanin production is continuous, so the skin is always pigmented to some degree. In these races the incidence of skin cancer is much lower because cells are constantly protected from UV radiation by melanin.

Melanocytes actually produce two different pigments: eumelanin (brown) and phaeomelanin (yellow and red). Red heads happen to produce more phaeomelanin and less eumelanin, which is why they don't tan very well. In albinos, the chemical pathway that produces melanin cannot proceed because an enzyme called Tyrosinaseis missing. Therefore albinos have no melanin in their skin, hair or irises.

 

If you are Caucasian and you don't have a tan, then the cells in your skin are not protected from the sun's ultraviolet radiation. You are therefore an easy target for sunburn if you spend too much time in the sun. As anyone who has a sunburn knows, sunburn leaves your skin red and extremely painful. In severe cases the skin forms blisters.

When you get sunburn, your skin is actually damaged by UV radiation and your body is responding to the damage. The body responds to the damage with increased bloodflow to the capillary bed of the dermis in order to bring in cells to repair the damage. The extra blood in the capillaries causes the redness -- if you press on sunburned skin it will turn white and then return to red as the capillaries refill.

How to prevent sunburn?

The best way to avoid sunburn is fairly obvious: Stay out of the sun. Specifically, avoid direct sunlight between the hours of 10 a.m. and 4 p.m., when UV light is most intense. If you must be outdoors, find shade. If you're heading to the beach, bring a sun umbrella to cast some shade when you're relaxing in the sand.

The American Academy of Dermatology recommends everyone use sunscreen that offers the following:
- Broad-spectrum protection (protects against UVA and UVB rays).
- Sun Protection Factor (SPF) 30 or greater.
- Water resistance.

A sunscreen that offers the above helps to protect your skin from sunburn, early skin aging, and skin cancer. Sunscreen does play an important role in protecting your skin from the sun, but it does not offer complete protection. To protect your skin and find skin cancer early, dermatologists recommend the following:

- Generously apply a broad-spectrum, water-resistant sunscreen with a Sun Protection Factor (SPF) of at least 30 to all exposed skin. “Broad-spectrum” provides protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Re-apply approximately every two hours, even on cloudy days, and after swimming or sweating. 

- Wear protective clothing, such as a long-sleeved shirt, pants, a wide-brimmed hat and sunglasses, where possible.

- Seek shade when appropriate, remembering that the sun’s rays are strongest between 10 a.m. and 4 p.m. If your shadow is shorter than you are, seek shade.5

- Use extra caution near water, snow and sand as they reflect the damaging rays of the sun, which can increase your chance of sunburn.

- Get vitamin D safely through a healthy diet that may include vitamin supplements. Don’t seek the sun.6

- Avoid tanning beds. Ultraviolet light from the sun and tanning beds can cause skin cancer and wrinkling. If you want to look tan, consider using a self-tanning product, but continue to use sunscreen with it.

- Check your birthday suit on your birthday. If you notice anything changing, growing, or bleeding on your skin, see a dermatologist. Skin cancer is very treatable when caught early.  

Credit: Discovery Fit & Health, AAD.org, How-to-do-Stuff, NASA