Raphael Blochle, MD
The composition of sunlight that is biologically important can be
separated into four general wavelength regions. Ultraviolet A (UVA), Ultraviolet B
(UVB), visible light and infrared. Visible light does not appear to be harmful
unless part of photosensitive drug reactions. Infrared originating from sunlight,
so far, does not seem to contribute to the risk of skin cancer, although non-solar sources
of infrared can cause skin tumors and cataracts. The spectrum of light that has
damaging effects is therefore essentially UV light. UVA's spectrum is between 315 and
400nm, and UVB's spectrum is between 280 and 315nm. These different wavelengths
penetrate the skin to different depths with ultimately different clinical
consequences. UVB makes up only a small percentage of the total UV and do not
penetrate as deeply as UVA, yet seem to be the major culprit of both melanoma and
nonmelanoma skin cancers. Thus, medically speaking, it is the most important
component of sunlight. UVB rays are becoming more abundant too as the ozone layer
gets more depleted. UVA, generally thought to be the safe part of the UV spectrum,
has now also been implicated with significant risks but not to the extent of UVB
radiation. UVA radiation mainly act by potentiating the carcinogenic effects of UVB
rays. UVA is even the main wavelength produced by tanning beds. Tanning salon
visits are estimated at one million a day and while there has been a strong push to ban
them, the FDA has yet to do so because the data is not yet definitive. It has also
been found that most people do not use enough sunscreen protection to completely
cover the body. According to Dermatology Times you should use 30g (1oz) of sunscreen
to do the job, yet most peoples sunscreen bottles last over a year.
UV causes direct cellular damage and alterations in the body's
immunologic functioning. Photochemical interactions occur from the absorption of the
various wavelengths by molecules such as proteins and DNA. Oxygen species can also
be produced, further contributing to the UV induced damage. After sufficient sun
exposure, an erythema, or sunburn, will appear. Caused mainly by UVB, it is an increase in
blood flow to the region. Continuing exposure to the UVB rays will cause
further signs of damage such as wrinkling and irregular pigmentation. Many
conclusive studies have shown that sunlight is the major causative agent of melanoma
formation, which has the highest rates not surprisingly close to the equator, since the
amount of UV rays hitting the earth is latitude dependent. Skin pigmentation also
has some protective capabilities. Fair skinned individuals do have a relative
deficiency of melanin in the skin, and are at increased risk of developing skin cancer.
UVB has been shown to suppress the human immune system which leaves it vulnerable to
bacterial or viral diseases that penetrate through or affect the skin. Viruses such as
herpes, HIV, and chickenpox can be activated or reactivated. Exposure may even
affect the efficiency of vaccinations against disease.
The following six steps have been recommended by
the American Academy of Dermatology and the Skin Cancer Foundation to help reduce the risk
of sunburn and skin cancer.
- Minimize exposure to the sun at midday and between the hours of
10a.m. and 3 p.m.
- Apply sunscreen with at least a SPF-15 or higher that protects
against both UVA and UVB rays, to all areas of the body that are exposed to the sun.
- Reapply sunscreen every two hours, even on cloudy days. Reapply
after swimming or perspiring.
- Wear clothing that covers the body and shades the face. Hats
should provide shade for both the face and back of the neck. Wearing sunglasses will
reduce the amount of rays reaching the eye by filtering as much as 80 percent of the rays,
and protect the lids of our eyes as well as the lens.
- Avoid exposure to UV radiation from sunlamps or tanning parlors.
- Protect children. Keep them from excessive sun exposure when
the sun is strongest (10 a.m. and 3 p.m.), and apply sunscreen liberally and frequently to
children six months of age and older. Do not use sunscreen on children under six
months of age -- instead severely limit their exposure to the sun.
Skin cancer is the most common cancer in the United States. It
affects over 600,000 individuals annually. Although there are many contributing
factors that can result in skin cancer such as heredity, elevation, and arsenic, sunburn
and UV rays are still the principal causes. Tanning occurs after exposure to UV
light and has a protective action to prevent more skin injury, yet tanning does not help
prevent skin cancer, so the belief that a tanned body is a healthy body is not exactly
correct Sunburns can also increase the risk substantially with each serious sunburn
increasing the risk up to 50%. Hereditary factors play an important role as well.
People of Northern European descent with fair-skin and a family history of skin
cancer, are more susceptible.
Melanoma is a malignant tumor which originates in the cells called
melanocytes. Melanocytes are found in the basal parts of the epidermis and produce
the melanin pigment in response to UV radiation which in turn protects the skin from
further sunburn damage. There are in the USA over 30,000 cases a year, and its
incidence is increasing 5% annually. Although it is the rarest of the 3 main skin
cancers, it causes 75% of the deaths from skin cancer. According to the American
Academy of Dermatology "One person dies from malignant melanoma every hour. The
overall incidence rate for the disease is increasing faster then any other cancer and by
the year 2000 an Americans lifetime risk of developing melanoma will be 1 in 75. The
disease is now the most commonly occurring cancer in females ages 30 - 34." The
USA Environmental Protection Agengy estimated in 1991 that over the next 50 years 12
million Americans will contract skin cancer and 200,000 will die from melanoma
alone. People at high risk of getting melanoma are those who frequently have
sunburns, red or blonde hair, blue eyes, family history of melanoma, and fair skin.
The staging of Melanoma depends on the depth of the tumor. Treatment, especially for
earlier stages is usually surgery, while others can be added such as chemo, immuno, and
radiotherapy. A promising new experimental treatment includes vaccine therapy.
Some forms of melanoma are estrogen dependant, so a doctor should asses the risk of
estrogen therapy. Others recommend the patients not to take vitamin C suspecting it
could accelerate melanoma growth.
Within the epidermis there are also other cells called Keratinocytes
that can also become malignant. This malignant tumor is called a squamous cell
carcinoma and if the tumor comes from the basal Keratinocytes it is a basal cell
carcinoma. Squamous cell carcinoma can appear in various forms, usually as nodules
or patches. It is the second most common skin cancer in Caucasians and occurs in
about 100,000 Americans per year. It has a risk of metastasis or spreading to other body
parts but not as much as melanoma. It is usually found on frequently sun-exposed
areas, like the face and upper extremities. The cancer has a high cure rate, especially if
detected early. Basal cell carcinoma, another non-melanoma carcinoma can appear as
a nodule on sun exposed areas. They are characterized by slow growth and late
metastasis and has a high cure rate when treated appropriately.
Actinic Keratosis is a skin condition that is premalignant.
The rough dry crusty texture makes it easily recognized by touch. This lesion can
even occasionally itch. The presence of such a lesion indicates that there has been
sun damage, so the lesion appears more commonly on the face, neck and hands.
Since it can be the first step towards skin cancer if not treated, squamous cell carcinoma
is often seen as a late complication.
Cancer development requires numerous additive genetic changes which
occur through the presence of DNA lesions that are not repaired. DNA damage
can be due to too much exposure of an exogenous agent or defects of normal DNA repair
mechanisms. Three such examples of clinically distinct disorders are xeroderma
pigmentosum (XP), Cockayne's syndrome (CS), and a photosensitive form of
trichothiodystrophy. These disorders are inherited in an autosomal recessive
fashion, are rare, but can lead to serious consequences, even death. Interestingly,
of these three diseases with defective DNA repair, only XP has an increased frequency of
skin cancer. XP is characterized by a genetic defect of DNA repair mechanisms
influenced by UV radiation from any source, but most commonly sunlight. The symptoms
of XP can include blindness, deafness, growth and mental retardation, high incidence of
eye and skin cancer, and frequent blistering and freckling on even slight sun
exposure. Fortunately it is a very rare disorder with less than 1000 recorded cases
world wide. It is a life threatening disease with no known cure. The exposure
to UV radiation causes additive and irreversible damage. These patients need to be
constantly inspected to check for tumors. Normally cells are remarkably efficient in
repairing damage done to its DNA. Repair enzymes (which are proteins) function by
first recognizing the damaged strand, then excising the damaged section, and lastly
filling in the gap with the bases that were originally there. How do the enzymes
know what was originally there? Human DNA is double stranded, and the sister strand
is always paired in a certain fashion, complimentary and anti- parallel, so that the
enzymes can deduce what bases to use when filling in. Exposure of a cell to UV
light can result specifically in a defect of the DNA known as pyrimidine dimers which can
hinder further DNA replication. The repair enzyme deficient in XP is usually called
UV specific endonuclease whose function is to recognize the damaged DNA. There are
currently a couple of trial therapies under way. One is a protein or enzyme therapy
by Applied Genetics Inc. in which a skin lotion is applied containing the missing
endonuclease. The other therapy soon to be attempted is gene therapy in which case
the cell could make the missing enzyme. This method however is still quite difficult
because it is very hard place genes in sufficient cells in a person to cause a noticeable
difference, and there would always be the risk of allergic reactions, for the body might
identify this new enzyme as foreign. In the meantime though most XP patients still
lead quite restricted lives. Early diagnosis and consequent intervention is key to
delay the onset of symptoms which can ultimately lead to death. Symptoms usually
start by age 1 or 2 with excessive freckling and easy sunburning. CS is another rare
disease in that repair of genes is defective after UV radiation and is characterized by
physical and mental retardation that becomes evident within the first few years of
life. There is hypersensitivity to UV light but no increase in skin cancer, although
survival beyond the second decade is not common.
Bloom's Syndrome is also related with sunlight exposure by skin
color changes becoming much more evident in sun exposed areas, but also with other more
severe problems such as respiratory illness, susceptibility to cancers, and short
stature. Bloom's occurs due to fragmented chromosomes. Chromosomes are the
part of cells that contain our DNA. Bloom's patients therefore should avoid
environmental exposures that precipitate chromosome fragility such as x-rays and
Another set of conditions that require protection from UV rays are
albinism and vitiligo. Albinism is a group of inherited conditions with little or
total absence of pigment in their eyes, skin or hair. According to the National
Organization for Albinos and Hypopigmentation (NOAH) one in 17,000 Americans have some
form of albinism. All forms have vision problems while some additionally have skin
and hair problems. Although most have blue eyes, the color of the iris can also be
red, violet, hazel, or even brown. The more understood form of albinism is due to
lack of an enzyme called tyrosinase which is needed to produce pigment, namely
melanin. The inheritance of the disease is usually in an autosomal recessive
fashion, meaning both parents must carry the defective gene to have a child with
albinism. Since the body has two sets of genes an asymptomatic person can have
normal pigmentation and yet carry the defective gene. If parents previously had a
child with albinism, genetic testing and counseling is possible via amniocentesis which
consists of placing a needle into the uterus for a fluid sample. Among the most
common eye conditions in albinism are rapid to and fro movements, ocular muscle imbalance,
bright light sensitivity, and visual problems. In general people with albinism have
a normal life span, although life threatening skin cancers do occur with a higher
frequency than the general population, especially if sun protection is not used. If
skin protection such as lotion is applied, people with albinism can experience the
outdoors like anyone else. Sunscreens should be at least SPF 20 - 30.
"SPF" meaning "sun protection factor" is a standard test number.
The SPF x 10 gives you the total number of minutes a person could theoretically sit in the
sun without burning. The concern is that the SPF system measures mainly UVB
protection, leaving out the much deeper penetrating UVA, so the FDA is considering adding
a second rating for it. Vitiligo is a skin disorder where white spots appear usually
bilaterally on the same location. The problem arises when the melanocytes are
killed by our own immune system, thus being classified as an autoimmune disease, and is
characterized by leaving patches of white areas on the skin. It sometimes runs in
families indicating that hereditary factors may play a role, and while most patients show
slow progression the problem can disappear altogether. It is estimated that 1% of the
population is affected, often manifesting itself with other autoimmune disorders such as
diabetes, Addison's, and pernicious anemia. It has even been known to occur in times
of severe stress. Vitiligo is more debilitating in dark skinned individuals, as the
changes become more apparent. Treatment of vitiligo has shown mixed results and
include cover-up cosmetics, UVA light treatment to gradually return color in the patchy
areas, and even transplanting melanocytes into the white areas. Some patients, instead of
trying to gain their color back, choose to remove the color from normal areas to attain a
uniform skin tone. This process, called depigmentation, is done via a prescription cream
called monobenzone, and is irreversible.
Besides skin conditions, UV radiation is also a factor in eye
conditions. The eye is one of the most radiation sensitive organs. Laboratory
studies show that chronic UVB exposure is a major factor of cataract formation. This
occurs over time due to absorbed UV radiation by the lens in the eye. Specifically, a
photochemical process occurs, causing denaturation of the lens proteins. As the lens
becomes more opaque, blindness results. Cataract formation is the major preventable
cause of blindness worldwide. People in tropical areas and young children are most
susceptible. The reason of child susceptibility is due to their less well developed
pigmentation of the eye. Vision loss due to UV can also occur by directly damaging
the retina or pterygium formation, which is a "fleshy" growth of the white of
the eye which can block vision. Exposure of the eye to UV can also induce melanoma
of the eye and photokeratitis. Photokeratitis is also known as sun blindness or welder's
flash, and is basically a painful burn on the surface of the eye. Protection from
these disorders is via sunglasses, although ironically exposure to the UV radiation may be
enhanced by sunglasses that poorly absorb UV because the pupil opens wider to compensate
for the reduced visible light.
One good point about sunlight is that it can produce vitamin D in
the skin. Vitamin D is considered both a hormone and a vitamin. It
participates in normal cell growth, and could play a role in cancer prevention. Vitamin D
also helps in the regulation of blood sugar by acting on insulin, and more importantly
calcium and phosphorus, enabling bone and teeth to harden. In vitamin D deficiency bones
soften to the point that they curve, a condition in children known as rickets and
osteomalacia in adults.
Ultraviolet radiation can be brought to good use if used
appropriately. It can be used as a germicidal agent. Bacteria in air or water can be
killed using UV radiation. Even more effective is the UV radiation used synergistically
with ozone. The two sterilants work together in a low cost reliable way.