Can a broken thermometer or light bulb cause mercury poisoning?

Some thermometers and light bulbs contain very small amounts of mercury. If you break one, it's unlikely to cause any health problems. However, you should avoid contact with the mercury and take extra care when cleaning it up.

What is mercury?

Mercury is a metal that's liquid at room temperature. It looks like silvery-white beads or balls (globules). Liquid mercury is sometimes called metallic or elemental mercury.

Liquid mercury can turn into a vapour (gas), so clean up a spill as safely and quickly as possible using the tips below.


The amount of mercury in a thermometer is very small, usually up to 3g.

Mercury thermometers are being phased out. You can use several other types of thermometer to take someone's temperature, such as digital thermometers, thermometer strips and ear thermometers. 

For more information about other types of thermometer, including how to use them, see How do I take someone's temperature? 

Light bulbs

Traditional tungsten or filament light bulbs don't contain mercury. These bulbs are being phased out and replaced with energy-saving light bulbs.

Some energy-saving light bulbs contain a tiny amount of mercury, sealed inside the bulb. In one bulb, there's usually less than 4mg (about enough to cover the tip of a ballpoint pen).

Fluorescent light strips or tubes, such as those sometimes used in kitchens and garages, also contain small amounts of mercury.

If these bulbs are unbroken, they can usually be recycled at your local recycling centre.  

What if I break a thermometer or light bulb?

If you break a mercury thermometer or light bulb, a small amount of liquid mercury may spill out. Liquid mercury can separate into small beads, which can roll some distance away. The mercury may also evaporate into vapour.

However, this small amount of mercury is extremely unlikely to cause problems for your health.

Some tips for cleaning up

It's sensible to take extra care when you clean up the mercury. Below are some tips to help you do this:

  • ventilate the room by opening the windows, for example – leave them open for at least 15 minutes 
  • go out of the room while it's being ventilated, making sure children and pets are kept out
  • wear rubber or plastic gloves and change into some old clothes before cleaning up the mercury beads and broken glass
  • pick up the pieces of glass carefully and put them in a plastic bag or container
  • collect the spilled mercury beads using a thin piece of card or a strip of masking tape – you can also use an empty plastic bottle to suck them up, such as an empty washing-up liquid bottle
  • mercury beads reflect light, so you can use a torch to look for any beads that are difficult to spot 
  • put the card (or bottle) and the mercury beads into the plastic bag
  • wipe the area with a damp cloth, then put the cloth in the same bag and seal it
  • leave the room to ventilate for at least 24 hours after cleaning the spill


Mercury spills on absorbent surfaces, such as carpets and upholstery, can be difficult to clean up. In these cases, it is advisable to get in contact with your local authority's environmental health department. The affected areas may need to be removed and disposed of in a particular way.

What not to do

When cleaning up a mercury spill:

  • don't put the sealed bag in your household bin, as mercury is classed as hazardous waste 
  • don't touch the mercury with your bare hands
  • don't use a vacuum cleaner
  • try not to create dust – if there is any dust, avoid breathing it in
  • don't put the mercury down the sink or the drain
  • don't sweep the mercury up with a brush
  • don't wash clothes with mercury on them in a washing machine – dispose of them in a sealed bag

Symptoms of mercury poisoning

Although mercury is poisonous (toxic), it usually only causes problems if you inhale large amounts of it. 

Very little mercury is absorbed by your body if you swallow a small amount of liquid mercury or get it on your skin for a short time. This is considered almost non-toxic and you'll probably have no symptoms. 

However, if you breathe in mercury vapour or globules, it can be absorbed into the bloodstream and cause symptoms such as:

Your eyes may be sore if mercury vapour gets into them. Your eyelids may also twitch and become red and swollen.

When to seek medical advice

You should contact your GP for advice if you have any of the symptoms above.

Wash your skin or eyes (removing any contact lenses first) with lukewarm water for at least 10-15 minutes if they come into contact with mercury.

Change your clothes and put any soiled clothes in a sealed bag.

You can also call NHS 111 for advice if you're not sure whether you need to see your GP.

Further information:

Page last reviewed: 06/07/2015

Next review due: 30/06/2018