Hey there catherine!! Yup, Julia’s got it. It all depends on how much melanin our skin produces. Some of us produce more of it than others, and the amount of it our body produces is dependent on UV exposure. UV is dangerous for us because it destroys our DNA. Damaged DNA means dead cells and that’s no good! Melanin is great because it absorbs UV light and reemits it a different wavelengths that aren’t harmful to our cells (basically it turns them to heat radiation – uummmm warm skin on a sunny day!).
Our bodies have a mechanism that stimulates melanin production when it senses DNA damage from UV. This leads to delayed development of a tan – the more melanin in your skin the darker it is!! So, people with really dark skin naturally have lots of melanin and don’t really tan. People with fair skin don’t have much melanin – so they can really burn! The sunburn is cells dying on our skin do to DNA damage. If we make melanin fast enough we can prevent it, but some of us just aren’t that good at it!! I know I really burn because my skin is fair!! Ouch!
As the others have said it is due to levels of melanin. I wish that I had some more as I can’t get a tan. You can buy it as a supplement and take it to make you tan but I have heard that it makes your insides orange (no idea if this is true though).
I am sitting with a doctor and he says he doesn’t really know why people burn – apparently the actual in detail mechanism of sunburn is not very well understood. But the others are right about the whole melanin thing. People with dark skin technically should burn less (except I have a friend who is darker than me – her Dad is from Mauritius – but she burns more than me….hmmm).
Anyway we get exposed to UV radiation in the sun and this can cause damage to our skin (sunburn) and skin cancer. UV radiation can cause breaks in our DNA and this is what makes us more cancer-prone. So, if you are out in the sun you should always wear sunscreen!!