Noticing blood in your wee isn't something you should ignore.
A new campaign from Public Health England, called 'Be Clear on Cancer', aims to raise awareness of the key symptom of bladder or kidney cancer - blood in urine.
The video above, which was made as part of the health campaign, features TV doctor and GP Dr Dawn Harper. She advises everyone to check their wee before they flush the toilet - every single time.
She also highlights the importance of seeing your doctor immediately, even if you notice just a small amount of blood in your wee.
Dr Harper explains that, if it contains blood, the colour of your wee can vary - it can be very diluted and a light pink shade or it can be the colour of a postbox. (See the colour chart below.)
Additionally, the blood might not show up every time you pee. In fact, it can happen just the once, which is why it's always important to check before you flush.
Blood in urine is a symptom in over half of bladder cancers and almost one fifth of kidney cancers.
Other symptoms of bladder cancer include: needing to wee more frequently, experiencing sudden urges to urinate and experiencing a burning sensation when you wee.
If the bladder cancer reaches an advanced stage and begins to spread, symptoms can include: pelvic pain, bone pain, unintentional weight loss and swelling of the legs.
Other symptoms of kidney cancer include: a persistent pain in your side (just below the ribs) and/or a lump or swelling in the area of your kidneys (on either side of the body).
Less common symptoms of kidney cancer include: extreme tiredness or anaemia, unintentional weight loss, a high temperature of 38C or above, night sweats, a general sense of feeling unwell, swelling of the veins in the testicles (in men, loss of appetite and high blood pressure).
Dr Harper concludes: "If you notice blood in your pee, your doctor will want to see you.
"Chances are it's nothing serious, but if it is bladder or kidney cancer, seeing your doctor early could save your life."