# An Odd Description of Skin Cancer Cause from UV Radiation

• Medical
• Buzz Bloom
In summary, a recent study found that skin cancer rates are higher in New Zealand compared to other countries due to the increased strength of UV radiation, which is 40% stronger in New Zealand than at comparable latitudes in the Northern Hemisphere. This is likely due to a combination of factors including reduced ozone concentration, decreased distance between the sun and Earth, and increased UV optical depth. However, further research is needed to fully understand the impact of these factors on UV radiation levels and skin cancer rates.
Buzz Bloom
Gold Member
TL;DR Summary
Quotes from a recent Scientific American will be in the main text. The primary quote is about New Zealand having a 40% stronger UV radiation exposure than places in the northern hemisphere. My effort at understanding the math produces a limit of only a 6.9% stronger UV exposure.
Scientific American
June 2, 2022
Vol 32 Number 6
Page 62
Title: Skin Cancer around the World
Two Quotes:

“The main cause of skin cancer is the exposure to the sun’s ultraviolet rays…”
“UV radiation is about 40% stronger in New Zealand than it is at corresponding latitudes in the Northern Hemisphere. Because of Earth’s tilt, the Southern Hemisphere is closer to the sun than the north is during its own summer. “

I am unable to find any basis for this difference other than that the distance of the sun to the Earth is greater when the Earth is at aphelion (152.1 x 10^6 km) than it is at perihelion (147.1 x 10^6 km).

The amount of sun UV radiation hitting the Earth is related to the Earth’s distance from the sun. If there are two distances being compared, say D1 > D2, then the ratio R of these two radiation densities is (roughly) approximately (D1/D2)^2, which is greater than 1. The larger these distances, then the more precise will be this approximate ratio.

Letting D1 be the aphelion distance and D2 the perihelion distance gives the result:
R = (152.1 / 147.1)^2 = 1.069.
This means that the Earth at perihelion has a radiation density 6.9% greater than the radiation density at aphelion. Seeing this 6.9% result I have not been able to understand how it is possible that the quote “UV radiation is about 40% stronger…” can possibly be correct.

I am hopeful that someone here at the Physics Forums will be able to educate me regarding my apparently incorrect understanding.

The increased amount of UV is due to a combination of several factors. Below is an incomplete list:

• Reduced ozone concentration in the upper atmosphere over New Zealand vs comparable latitudes in the north.
• Decreased distance between the Sun and the Earth during New Zealand summers.
• Possibly reduced UV absorbing aerosols compared to northern latitudes.
• Increased UV optical depth (less absorption of UV) at lower altitudes.
Quote from the 2nd of my references below:
Peak UV intensities in the New Zealand site (45 degrees S, alt. 0.37 km) exceed those at comparable latitudes and altitudes in North America by 41 +/- 5%, and are more comparable with those over 1 km higher and 5 degrees closer to the equator.

From the third reference:
UV in New Zealand is relatively high compared with corresponding northern latitudes, due to its lower summer ozone amounts, closer Earth-Sun separation in summer, and unpolluted air.

Refs:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL037141
https://pubmed.ncbi.nlm.nih.gov/16520871/
https://aip.scitation.org/doi/pdf/10.1063/1.4975499

russ_watters, berkeman, Tom.G and 2 others
Drakkith said:
The increased amount of UV is due to a combination of several factors. Below is an incomplete list:

• Reduced ozone concentration in the upper atmosphere over New Zealand vs comparable latitudes in the north.
• Decreased distance between the Sun and the Earth during New Zealand summers.
• Possibly reduced UV absorbing aerosols compared to northern latitudes.
• Increased UV optical depth (less absorption of UV) at lower altitudes.
Quote from the 2nd of my references below:
Peak UV intensities in the New Zealand site (45 degrees S, alt. 0.37 km) exceed those at comparable latitudes and altitudes in North America by 41 +/- 5%, and are more comparable with those over 1 km higher and 5 degrees closer to the equator.

From the third reference:
UV in New Zealand is relatively high compared with corresponding northern latitudes, due to its lower summer ozone amounts, closer Earth-Sun separation in summer, and unpolluted air.

Refs:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL037141
https://pubmed.ncbi.nlm.nih.gov/16520871/
https://aip.scitation.org/doi/pdf/10.1063/1.4975499
I would suggest peoples behaviour and lifestyle may be more important than all of these. In Australia there was a very visible campaign to use sun screen, wear hats and avoid over exposure, this might be why the rate is now higher in New Zealand.

Laroxe said:
I would suggest peoples behaviour and lifestyle may be more important than all of these. In Australia there was a very visible campaign to use sun screen, wear hats and avoid over exposure, this might be why the rate is now higher in New Zealand.
While perhaps true, this doesn't explain the increase in UV radiation itself, merely another reason why rates of UV related skin diseases are higher.

It is a bit strange but the differences may be less significant than we think. There have been a number of explanations, the favourites appear to be low levels of air pollution and air coming off Antarctica during the summer months which is low in ozone. I thought this site was interesting, even though it doesn't seem very impressed with the ozone idea, but this does seem to be mentioned in most other sources.
https://www.ehinz.ac.nz/indicators/uv-exposure/daily-uv-levels/

## What is UV radiation and how does it cause skin cancer?

UV radiation is a form of electromagnetic radiation emitted by the sun and artificial sources like tanning beds. It includes UVA, UVB, and UVC rays, with UVA and UVB being the main contributors to skin damage. UV radiation causes skin cancer by damaging the DNA in skin cells, which can lead to mutations and the development of cancer if the damage is not properly repaired.

## Are certain types of UV radiation more harmful than others?

Yes, UVB rays are often considered more harmful in causing skin cancers because they have more energy and can cause direct DNA damage. UVA rays, which penetrate deeper into the skin, contribute to skin aging and indirect DNA damage, which can also lead to cancer. Both types are dangerous and protective measures should be used against exposure to both UVA and UVB rays.

## Can wearing sunscreen really protect against skin cancer?

Yes, sunscreen is effective in protecting against skin cancer. It works by absorbing, reflecting, or scattering sunlight, thereby reducing UV radiation exposure. For best protection, it's recommended to use a broad-spectrum sunscreen with an SPF of 30 or higher, reapplying every two hours or after swimming or sweating.

## How often should one perform skin checks for cancer signs?

It is advisable to perform a self-examination of your skin every month to check for any new moles or changes in existing moles, including changes in size, shape, color, or texture. Additionally, seeing a dermatologist for a professional skin exam annually or more often if you're at high risk is recommended.

## Does having a tan protect you from UV radiation?

No, having a tan does not adequately protect you from UV radiation. A tan is actually a sign of skin damage, as it occurs when the skin produces additional pigment to protect itself against prolonged exposure to UV rays. This minimal protection is equivalent to an SPF of about 2 to 4, which is significantly lower than what dermatologists recommend for effective protection.

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