Skin care Flashcards
what is ultraviolet radiation?
a high-energy form of light present in sunlight
UV-A
longest wavelength and is not absorbed by the ozone
penetrates the skin deeper than UV-B
UV-B
responsible for sunburns
partially blocked by the ozone layer
UV-C
totally absorbed by Earth’s atmosphere
we encounter it only from artificial radiation sources
what can exposure to UV light result in?
molecules gaining enough energy for bonds to be broken.
UV damage
because UV has enough energy to break chemical bonds, over-exposure can lead to the breakdown of important organic molecules within our body
what do UV-A and UV-B cause?
UV-A - sunburn
UV-B - skin ageing
both can cause skin cancer
sunburn
- skin becomes inflamed and red in response to overexposure to UV (typically UV-B)
- skin may peel to get rid of any damaged cells
photoaging
- UV-A and UB-B exposure cause the collagen in the skin to breakdown.
- As the skin attempts to repair itself it does so imperfectly and solar scars form. This forms wrinkles.
skin cancer
- UV light can damage DNA cells and stop them from functioning correctly
- These mutations to the genetic material can cause cancerous growths seen in skin cancer
sunscreen
- contain compounds that filter the UV light so that less UV reaches the skin
- contain organic compounds which absorb the UV light and dissipate the energy as heat before it can penetrate into your skin and damage cells.
sunblocks
- contain compounds that reflect the UV light so it does not reach the skin at all
- contain inorganic compounds like zinc oxide or titanium dioxide
what happens when UV light breaks bonds
free radicals are formed
what are free radicals
the atoms formed which have unpaired electrons and, as a result, are highly reactive
free radical reactions
-UV light has enough energy to break apart a covalent bond forming two atoms with unpaired electrons
free radical chain reaction
free radicals are unstable due to unpaired e- and so react very quickly with any other chemical nearby to form new bonds.
3 steps in free radical chain reactions
- initiation
- propagation
- termination
Initiation
the UV light causes some of the Cl-Cl bonds to break
2 free radicals on the RHS
Propagation
highly reactive free radicals react with hydrogen molecules forming H-Cl and a hydrogen radical which can react with chlorine molecules
1 free radical on each side
Termination
The free radicals react with other radicals to form stable substances. This terminates (stops) the process
2 free radicals on LHS
reactions of alkanes with halogens
alkanes will decolourise bromine when UV light is present in free radical reactions
what are free radical scavengers?
molecules that can react with free radicals to form stable molecules and prevent chain reactions
what are free radical scavengers added to?
- cosmetics (eg: anti ageing creams, vit. C/E
- food products (eg: antioxidants, slow down oxidation)
- plastics
examples of natural free radical scavengers
melatonin and vitamin E
