Sunburn is a form of burn that is caused by radiation from the Sun that affects living tissue especially skin, that results
from an overexposure to ultraviolet(UV)
radiation. The general symptoms in humans include reddish skin that
is sensitive to the touch,discomfort, tiredness, and mild dizziness. An excess of UV
radiation may leads to life-threatening skin cancer in extreme cases

Sunburns is different from thermal burns, which result
from infrared radiation.Infrared radiation provides sunlight its warmth, it is
not the heat of the sun that burns the skin. A sunburn manifested by cutaneous
redness, swelling and pains caused by exposure to the sun’s ultraviolet
radiation,UVA and UVB.

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Ultraviolet (UV) is an electromagnetic
radiation with wavelength from
10 nm to 400 nm, shorter than that of visible light. UV radiation constitutes about 10% of
the total light output of the Sun, and is thus present in sunlight.

These wavelengths are classified as UVA, UVB, or UVC,
with UVA the longest of the three at 320-400 nanometers. UVB ranges from 290 to
320 nm. The shortest wavelength among them is UVC and most UVC is absorbed by
the ozone layer and does not reach the earth.

However,both UVA and UVB penetrate the atmosphere and
play an important role in skin conditions such as premature skin aging, eye
damage, and mostly sunburn. They also suppress the immune system, reducing your
ability to fight off these and other maladies.

The energy from ultraviolet radiation can damage
molecules in the skin, specifically DNA. The effect of this is the synthesis of
different proteins and enzymes. The effects of these proteins, prostaglandins
and cytokines, lead to dilation of the cutaneous blood vessels and a accumulation
of inflammatory cells. This results to redness, swelling and pain. When the
skin is exposed to excessive radiation exposure, it generally takes four to six
hours for these proteins to generate.The body does have mechanisms to repair
damaged DNA after ultraviolet exposure. But as the frequency of sunlight
exposure increases,the probability of some of damage will not be repair. This
mutated DNA may eventually lead to skin cancer.

 

The two major wavelength which damages the skin:

UVA, which penetrates
the skin more deeply than UVB, play a major part in skin aging, but recently
scientists believed it did not cause significant damage in the epidermis which
is outermost skin layer where most skin cancers occur.This
wavelength,however,started the process of sunburn.

UVB, the main cause of
skin reddening and sunburn, tends to damage the skin’s more superficial
epidermal layers. It plays a key role in the development of skin cancer and a
contributory role in tanning and photoaging. Its intensity varies by season,
location, and time of day.

 

How sunburn occurs:

The damage is recognized by the body,
which then triggers several defense mechanisms, including protein to revert the
damge and peeling to remove damaged skin cells, and increased melanin
production to prevent future damage. Melanin absorbs UV wavelength light,
acting as a thin bulletproof vest from the a bombard of UV. By preventing UV
photons from disrupting chemical bonds, melanin alters the DNA and the
generation of mutated
cells.

Sunburn causes an inflammation process, that started the production of prostanoids and bradykinin. These chemical compounds increase sensitivity to heat by reducing the
threshold of heat receptor activation from 109 °F (43 °C) to
85 °F (29 °C).The pain may be caused by overproduction of a protein
called CXCL5, which causes the
activatation of nerve fibres

 

Why do sunburns give off heat?

Radiant energy can be viewed as photon energyThe energy carried by each photon is proportional to its
frequency. When EM waves are absorbed by
an object, the energy of the waves is converted to heat. For example,sunlight warms surfaces that it irradiates.

When our skin is exposed to
sunlights,we are also exposed to these photons which carries photon energy.Upon
contact with our skin,by abiding the Law of thermodynamics which states that the
energy can not be destroyed but it can be changed,the photon energy changed
from radiant energy to heat.

 

The warmth of a sunburn comes from increased blood
flow to the exposed part of the skin

Blood is rushing to the affected area because of the
inflammation to begin the process of repairing the damaged cells by removal and
replacement of damaged cells and that is where the sensation of heat radiation
comes from.

 

Heat as moving light = radiation

• Radiation is the heat transfer by electromagnetic
waves or known as thermal light waves.These waves are invisible to the naked eyes

• thermal radiation is a small part of the
electromagnetic spectrum.

Infrared radiation is popularly known as “heat
radiation”, but light and electromagnetic waves of any frequency will heat
surfaces that absorb them

Heat is energy in transit that flows due to
temperature difference. Unlike heat transmitted by thermal
conduction or thermal convection, thermal radiation can propagate
through a vacuum and space. Thermal radiation is characterized by a
particular spectrum of many wavelengths that is associated with emission from
an object, due to the vibration of its molecules at a given temperature.