Bacteria and fungi exist naturally in the air and remain invisible to the human eye.

However, they grow quickly and become more visible in warm, moist environments especially when they have a source of nutrients. Typical forms of nutrients include shampoo, soap, spray from aerosols, washing powder, household dust and food.

This visible black slime or staining is called a biofilm.

Bathrooms and kitchen are ideal places for biofilms to grow.  They will form more readily on rough surfaces, such as limescale.

Common places include the inside of cold taps where they can form a slimy or jelly like deposit which hangs from the end of the tap.

They can also be found:

• Around the base of tap fittings
• In showerheads or on shower curtains
• On tile grout
• In drains or plugholes
• In toilet cisterns or bowels
• In washing machines, particularly around the powder draw or door rim
• In refrigerator drip trays or ice making machines
• In drinks vending machines
• In dehumidifiers
  

While unsightly, biofilms do not generally pose a risk to health. Some may cause an allergic reaction in susceptible people.

There are three easy steps to dealing with biofilms:

• Improve ventilation

This will allow damp areas in kitchens and bathrooms to dry quickly. Open a window after showering or cooking, install an extractor fan or keep trickle vents open in double glazing. Using a dehumidifier can also help.

Routinely clean all surfaces which can be affected

Taps: Black slime associated with tap fittings can be easily removed by cleaning inside the tap with a small brush (or old toothbrush) dipped in a mild bleach solution. You should run water to flush the tap before use.

Kitchen surfaces: These can be wiped down with a household cleaner or a mild bleach that will kill the bacteria and fungal spores.

Tile grouts, silicon sealers, shower curtains and rubber materials: In addition to a household cleaner, mould and mildew cleaner is also particularly effective. If growths are not removed on a regular basis they can cause permanent staining.

Limescale: Remove using a standard household cleaning product or a solution of bicarbonate of soda.

Washing machines: Running the washing machine at 60˚C or above regularly will kill the microbes. Leave the powder drawer and door open after use to allow it to dry out between loads.

Fridges: Clean, and change filter cartridges according to the manufacture’s guidelines.

Water filters and softeners: These can encourage biofilm growth. Make sure they are serviced according to the manufacturer’s instructions.

Ensure fittings can be easily cleaned. For example, when purchasing taps try and avoid ones with plastic inserts as these are commonly associated with biofilms. If your taps do have plastic inserts or detachable fittings they should be regularly removed, cleaned and disinfected.