Indirect DNA damage occurs when a
UV-photon is absorbed in the human skin by a
chromophore
A chromophore is the part of a molecule responsible for its color. The word is derived .
The color that is seen by our eyes is that of the light not Absorption (electromagnetic radiation), absorbed by the reflecting object within a certain wavele ...
that does not have the ability to convert the energy into harmless heat very quickly.
Molecules that do not have this ability have a long-lived
excited state
In quantum mechanics
Quantum mechanics is the fundamental physical Scientific theory, theory that describes the behavior of matter and of light; its unusual characteristics typically occur at and below the scale of atoms. Reprinted, Add ...
. This long
lifetime leads to a high probability for reactions with other molecules—so-called bimolecular reactions.
and
DNA
Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
have extremely short excited state lifetimes in the range of a few femtoseconds (10
−15s).
The excited state lifetime of compounds used in
sunscreens
Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...
such as
menthyl anthranilate,
avobenzone or
padimate O is 1,000 to 1,000,000 times longer than that of melanin,
and therefore they may cause damage to living cells that come in contact with them.
The molecule that originally absorbs the UV-photon is called a "chromophore". Bimolecular reactions can occur either between the excited chromophore and DNA or between the excited chromophore and another species, to produce
free radicals and
reactive oxygen species. These reactive chemical species can reach DNA by diffusion and the bimolecular reaction damages the DNA (
oxidative stress
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...
). Unlike direct DNA damage which causes sunburn, indirect DNA damage does not result in any warning signal or pain in the human body.
The bimolecular reactions that cause the indirect DNA damage are illustrated in the figure:
:
1O
2 is reactive harmful
singlet oxygen
Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemistry, inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are Radical (chemistry), spin p ...
:
:
Location of the damage
Unlike
direct DNA damage, which occurs in areas directly exposed to UV-B light, reactive chemical species can travel through the body and affect other areas—possibly even inner organs. The traveling nature of the indirect DNA damage can be seen in the fact that the
malignant melanoma can occur in places that are not directly illuminated by the sun—in contrast to
basal-cell carcinoma and
squamous cell carcinoma, which appear only on directly illuminated locations on the body.
See also
*
Free radical damage to DNA
*
Photoprotection
*
Sunscreen
Sunscreen, also known as sunblock, sun lotion or sun cream, is a photoprotection, photoprotective topical product for the Human skin, skin that helps protect against sunburn and prevent skin cancer. Sunscreens come as lotions, sprays, gels, fo ...
References
{{reflist
Photochemistry
Skin conditions resulting from physical factors
Sun tanning