Caves are potentially dangerous  places.  Cavers should be aware of this, but some hazards are less obvious, invisible and may be intermittent in nature. Some of these are described below.

Leptospirosis (Weil's Disease)

A potentially fatal bacterial infection transmitted in water contaminated by infected animals.

More details available from the BCA and NHS.

Carbon Dioxide (CO2)

A colourless, odourless gas which can cause an acidic taste in high concentrations.

Symptoms: increased breathing rate, especially when exerting, headache, raised heart rate.

Carbon Monoxide (CO)

An odourless, colourless, tasteless gas, toxic at very low levels.

Binds with haemoglobin, reducing the blood's ability to transport oxygen.

Symptoms: headache, nausea, tiredness and dizziness.

Symptoms do not reduce on return to fresh air.

Radon (Rn)

An odourless, colourless, tasteless gas.

No noticeable short term symptoms, but long term exposure, accumulated over many underground trips, can eventually cause lung cancer.