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Every fact here comes from a trusted cancer charity or health body. The simulations are tested against them.
Do the simulations match the science?
23 of 23 checks pass. Each one runs the teaching model and checks it behaves the way the sources say.
- Chemo affects fast-dividing cells (cancer and hair follicles) far more than slow-dividing cells.Why chemo causes hair loss
- Healthy fast-dividing cells recover after treatment stops.Why chemo causes hair loss
- The wrong idea 'chemo only touches cancer' leaves the hair cells untouched, so the simulator can tell it apart.Why chemo causes hair loss
- Doubling gives exponential growth: after 15 doublings there are 2^15 times as many cells.How tumours grow
- A doubling cluster stays tiny for a long time, then grows fast: the second half adds far more than the first.How tumours grow
- The wrong idea 'it grows steadily' adds the same amount in each half of the watch.How tumours grow
- Crowded normal cells stop dividing once the dish is full.Cells out of control
- Cancer cells ignore the stop signal and keep dividing past the dish's room.Cells out of control
- In the contact test nothing crosses to the other dish, after a short or a long touch: cancer isn't caught.Can you catch cancer?
- The wrong idea 'cancer is catching' sends cells across at once, so the simulator can tell it apart.Can you catch cancer?
- Cloud cover reduces UV but never removes it.UV on a cloudy day
- Ordinary cloud lets over 90% of the UV through, and even full cover lets most through.UV on a cloudy day
- Damage to skin cells adds up with time in the UV, and sun protection cuts it.UV on a cloudy day
- The wrong idea 'clouds block UV' lets almost none through, so the simulator can tell it apart.UV on a cloudy day
- Where beams from different angles meet, their doses add up: the tumour gets about as much from five weaker beams as from one strong beam.Radiotherapy beams
- One strong beam also gives the healthy tissue on its path a high dose, more than the tumour gets.Radiotherapy beams
- Spreading the beams all around gives each healthy spot much less than one strong beam, so the spread plan is judged best with 3 to 9 beams.Radiotherapy beams
- Spreading the dose across more beams (3, then 5, then 9) gives each path less where the beams go in.Radiotherapy beams
- The wrong idea 'weak beams don't add up' picks one strong beam, so the simulator can tell it apart.Radiotherapy beams
- With or without a change from birth, and with fewer or more exposures, most of a cell line's changes appear during life.Born with it?
- A change from birth is a head start: the cell line reaches its five changes sooner, but still needs changes during life.Born with it?
- Fewer everyday exposures mean fewer changes during life.Born with it?
- The wrong idea 'cancer is mostly passed down' puts most changes at birth, so the simulator can tell it apart.Born with it?
Sources
41 facts, from the World Health Organization, the National Cancer Institute, Cancer Research UK and the American Cancer Society. Each one was checked on its page; 20 back the experiments directly.
Chemotherapy works by killing cancer cells and other fast-growing cells, or stopping them from growing.
National Cancer InstituteChecked 28 October 2026
Chemotherapy damages cells that are dividing. Cancer cells divide much more often than most normal cells, so chemotherapy can damage and destroy them.
Cancer Research UKChecked 28 October 2026
Chemotherapy can also kill or slow healthy cells that grow and divide quickly, such as cells lining the mouth and intestines and the cells that make hair grow.
National Cancer InstituteChecked 28 October 2026
The normal cells most likely to be damaged by chemo are blood-forming cells in the bone marrow, hair follicles, and cells in the mouth, digestive tract and reproductive system.
American Cancer SocietyChecked 28 October 2026
Some types of chemotherapy make hair fall out, on the head and on other parts of the body.
National Cancer InstituteChecked 28 October 2026
Chemotherapy kills fast-growing cells, including the cells in hair follicles, which is why some chemo can cause hair loss or thinning.
American Cancer SocietyChecked 28 October 2026
After chemotherapy, hair often grows back 2 to 3 months after treatment has ended.
National Cancer InstituteChecked 28 October 2026
Most hair loss caused by chemo is reversible once treatment is over.
American Cancer SocietyChecked 28 October 2026
Normal cells can replace or repair the healthy cells that chemotherapy damages, so the damage to healthy cells doesn't usually last.
Cancer Research UKChecked 28 October 2026
Chemotherapy side effects often get better or go away after treatment is finished.
National Cancer InstituteChecked 28 October 2026
Unlike normal cells, cancer cells don't stop growing and dividing when there are enough of them, so they keep doubling and form a lump (tumour) that grows in size.
Cancer Research UKChecked 28 October 2026
Cancer cells ignore the signals that normally tell cells to stop dividing or to die.
National Cancer InstituteChecked 28 October 2026
Normally, cells grow and multiply by cell division to make new cells as the body needs them; old or damaged cells die and new cells take their place.
National Cancer InstituteChecked 28 October 2026
Cells send chemical messages to each other so that they stop growing and dividing when growth or healing is complete.
Cancer Research UKChecked 28 October 2026
A cell doubles by dividing into two: two cells become four, and so on.
Cancer Research UKChecked 28 October 2026
Abnormal or damaged cells that keep multiplying may form tumours, which are lumps of tissue.
National Cancer InstituteChecked 28 October 2026
Cancer is caused by changes to genes that control how cells work, especially how they grow and divide.
National Cancer InstituteChecked 28 October 2026
In general, cancer is not contagious: it does not easily spread from person to person.
National Cancer InstituteChecked 28 October 2026
You can't catch cancer from someone else; close contact such as touching, holding hands, sharing meals or breathing the same air can't spread it.
American Cancer SocietyChecked 28 October 2026
Cancer screening looks for cancer before symptoms appear, when cancer may be easier to treat.
National Cancer InstituteChecked 28 October 2026
When cancer is found at an early stage, treatment is more likely to be successful.
Cancer Research UKChecked 28 October 2026
Cancer screening is for people with no symptoms; it looks for possible signs of cancer before they are noticeable.
Cancer Research UKChecked 28 October 2026
Clouds block some UV, but over 90% of UV rays can still pass through cloud and cause sunburn.
Cancer Research UKChecked 28 October 2026
UV levels are highest under cloudless skies but can be high even when it is cloudy.
World Health OrganizationChecked 28 October 2026
UV radiation can't be seen or felt.
World Health OrganizationChecked 28 October 2026
You can't feel UV rays, so the temperature outside doesn't tell you whether you're at risk of skin damage; the warmth you feel is infrared.
Cancer Research UKChecked 28 October 2026
Too much UV from the sun or sunbeds can damage the DNA in skin cells; if enough damage builds up, cells can grow out of control and lead to skin cancer.
Cancer Research UKChecked 28 October 2026
Too much UV exposure is the main cause of skin cancer in the UK.
Cancer Research UKChecked 28 October 2026
Skin cancer is highly preventable. WHO recommends limiting time in the midday sun, seeking shade, wearing protective clothing, a broad-brimmed hat and wraparound UV-blocking sunglasses, and using broad-spectrum sunscreen on skin that clothes can't cover.
World Health OrganizationChecked 28 October 2026
Cancer Research UK's three sun-safety steps: spend time in the shade, cover up with clothes, a wide-brimmed hat and UV-protection sunglasses, and apply sunscreen (at least SPF 30, 4 or 5 stars).
Cancer Research UKChecked 28 October 2026
External beam radiation therapy comes from a machine that aims radiation at the cancer.
National Cancer InstituteChecked 28 October 2026
The external beam machine does not touch you, but can move around you and send radiation to part of your body from many directions.
National Cancer InstituteChecked 28 October 2026
When many small beams are aimed at a tumour from different directions, each beam has very little effect on the tissue it passes through, and the dose is delivered where they all meet.
National Cancer InstituteChecked 28 October 2026
Radiation can also affect nearby healthy cells, and damage to healthy cells can cause side effects.
National Cancer InstituteChecked 28 October 2026
The treatment team carefully plans radiotherapy to give a high dose to the cancer while sparing as much healthy tissue as possible.
Cancer Research UKChecked 28 October 2026
Gene changes that cause cancer can be inherited, can come from things in the environment, or can happen because of errors when cells divide.
National Cancer InstituteChecked 28 October 2026
Most cancers (90 to 95 percent) are caused by gene changes that happen during a person's lifetime, from ageing and from things in the environment.
National Cancer InstituteChecked 28 October 2026
Some popular ideas about cancer are scientifically wrong but can seem to make sense, and wrong ideas can cause needless worry and get in the way of good prevention and treatment decisions.
National Cancer InstituteChecked 28 October 2026
When people don't know how cancer develops, they may wrongly believe it can spread between people, which can cause fear.
American Cancer SocietyChecked 28 October 2026
Stories about cancer causes are popular in the news and on social media, but some things people hear, read or see are not supported by good evidence.
Cancer Research UKChecked 28 October 2026
This is for learning, not medical advice. If you have questions about cancer or your health, talk to a parent, teacher or doctor.