text: Every owner of a gadget piloted via a touchscreen has spent time rubbing it with a tissue, a cloth or a sleeve gripped round the heel of the hand to banish those unsightly marks.
  It's not that human fingers are filthy. Those smears come about thanks to a mix of physiology and good grooming habits, said Steve Block, an electronics industry scientist at Dow Corning, which makes coatings that get applied to touchable screens.
  "There's a whole range of things that can contaminate those surfaces," he said. "There are natural oils on the fingers as well as the lotions people put their hands. Then there's cosmetics and the times when you hold your telephone up to your ear and it's sweaty."
  Small wonder then that the sight of those smears is unsettling.
  Thankfully, there is no reason to fret, as those smears are safe if your touchscreen gadget is kept just for you, said Prof  Charles Gerba, a microbiologist at the University of Arizona.
  "Touchscreens are a source of a wide range of microbes, but not much of an issue if you do not share it among other people - since, if you are the only one using it, it's only your germs," he told the BBC.
  Sadly, that is not the case when those touchscreens are put to more promiscuous use, such as in a supermarket at the self-checkout, by patients in a doctor's waiting room or in a family that passes the gadget around.
  Studies by Prof Gerba and colleagues have shown how important an infection vector touchscreens can be when used by lots of people.
  "We have traced the spread of MRSA skin infection among teenagers that shared a cell phone," he said. "You will find MRSA on touchscreens on self-checkout screens in grocery stores in the US."
  Touchscreens can be "reservoirs of opportunistic pathogens", said Prof Gerba in a small-scale study that uncovered MRSA, E. coli and C. difficile and many others on screens in hospitals and supermarkets.
  It is worth keeping those surfaces clean, said Prof Gerba, even if the chances of getting ill are pretty low.
  "For viruses it can take as little one to make you ill, but this varies a lot depending on the organisms. Some bacteria take 100,000 cells to cause illness, others a few hundred," he said. "It just depends if you come across the right organisms at the right time."
  The study was carried out to test the best way of keeping those screens clean and killing off the bad bugs. The good news is that wipes impregnated with sodium hypochlorite (bleach), did a good job of disinfecting the screens. However, regularly wiping with bleach might not be a solution that domestic owners of very shiny, very expensive gadgets would favour.
  Thankfully, other fixes are at hand.
  To begin with, said Mr Block, screen makers are constantly refining the materials and coatings that make gadgets easy to wipe and keep clean. Those transparent coverings are glass, he said, but of a very particular type. Typically, he said, they and the coatings covering them are engineered to the most minute scale.
  "They are made of very specialised molecules that are designed for these type of applications," said Mr Block. The silicone coatings that are now becoming standard are far more resistant to the secretions and substances that can end up on a touchscreen.
  Also, said Mr Block, they are tougher and ensure a screen will stay responsive years after it is bought.
  There are other innovations that might help too. Japanese materials company Toray has come up with a coating that, it claims, repels up to 50% more of the oil and other residues found on fingers. In addition, once applied, the coating dries into millions of tiny wrinkles that help hide smudges to help screens stay sharp.
  The fourth generation of Gorilla Glass, which is used on many touchscreen gadgets, will include an antibacterial coating that can kill those pesky bugs by themselves. That coating is likely to start being used within the next couple of years.
  Then there is the work of scientists at Harvard University's School of Engineering and Applied Sciences, who turned to a carnivorous plant to develop their screen coating. They found that the walls of the pitcher plant are slippery because they are covered with tiny bumps that trap water. Insects that can easily walk on walls struggle to make any progress on this surface because it repels the oils on their feet.
  By mimicking this surface and applying an ultra-thin layer of lubricant, the researchers created a surface inimical to bodily substances. The work is still in the lab but is more evidence that those screens are only going to get harder to smear and easier to use.
  "Any dirt is a barrier between user experience and a display," said Mr Block.
target: Touchscreen tablets and phones are popular in almost every respect but one - the smears that fingers leave on the screen.