What can bright or dark yellow urine mean?

Urine becomes darker when it contains less water, which can happen after sweating, vomiting, diarrhoea, fever, or simply drinking less. Bright yellow urine may follow a vitamin supplement or strongly coloured food. Heat exhaustion and dehydration can produce darker urine alongside thirst, dry mouth, headache, dizziness, or reduced urination. Brownish urine, pale stools, yellow skin or eyes, abdominal pain, or marked tiredness can signal a liver or bile problem such as hepatitis and should not be explained away by hydration alone.

Drink fluids regularly unless a clinician has told you to restrict them. After heat or heavy sweating, move to a cool place, rest, and follow appropriate rehydration advice. Notice whether the colour changes after a supplement is taken and check the label rather than stopping prescribed treatment without guidance. Keep track of urine frequency and accompanying pain, fever, burning, nausea, or changes in stool or skin colour. Arrange a review if the change persists despite normal drinking.

Get urgent help for confusion, fainting, severe weakness, inability to keep fluids down, very little urine, or signs of serious heat illness. Prompt medical assessment is needed for yellow eyes or skin, severe abdominal pain, fever with feeling very unwell, blood in urine, or dark urine with muscle pain after intense exertion.

Ask whether your medicines, supplements, hydration, liver, or kidney function could explain the colour. Tell the clinician when it started, how often you urinate, recent heat exposure or illness, and whether your stools, skin, or eyes have changed.