Mud therapy may help to replenish the beneficial bacteria in our skin microbiomeMichael Zegers/imageBROKER.com GmbH & Co. KG/AlamyLook under the microscope at any square centimetre of human skin and you will find it teeming with bacteria, fungi, mites and viruses. It might sound yucky, but your skins microbiome is an important defence against invading pathogens.Because there are all these bacteria already there, its quite hard for a pathogen to get a foothold, says Catherine ONeill, a dermatologist at the University of Manchester, UK, and chief science officer of AxisBiotix, a company that offers skincare products based on microbiome research. Bacteria can also wage warfare on each other by secreting different chemicals that inhibit the growth of pathogens.Trained immunityThe skin microbiome, together with the gut microbiome, also helps train our immune system during childhood, teaching it to attack pathogens and ignore harmless stimuli. This could explain why people who have a greater diversity of skin bacteria are less likely to have allergies.Beneficial skin bacteria could also be the key to maintaining a smooth, wrinkle-free appearance. Our skin is like a fortress constructed from layers of skin cells packed together. In between the cells are lipids that keep the skin supple and plump, and certain bacterial species help to replenish those stores.Cutibacterium stimulates the skin to produce sebum, which protects the skin, reduces water loss and increases hydration, says Holly Wilkinson, who studies wound healing at the University of Hull, UK. Staphylococcus epidermidis and Streptococcus thermophilus