Here's a prickly choice for you. Would you rather have a tiny shard of broken glass stuck in your fingertip, or a little sliver of wood? If you had to pick you might prefer the wood, right? After all, wood is softer and natural and glass is like nothing but sharp edges. But the fact is, as far as your immune system is concerned, splinters made of organic matter can pose a bigger threat than a chip of glass or sliver of metal.

Of course when anything gets under your skin, your body's immune system will react to the invasion. The tissues around the injury will get inflamed, becoming red and swollen as blood and immune cells rush to the site. But if it's a big object like a splinter and the cells can't break it up and get it out, the next best thing is to wall it off from the rest of the body. White blood cells will surround it forming a barrier known as a granuloma to keep it from going anywhere.

But glass and metals are inorganic. They're not made from the tissue of a living thing so they won't cause as much of an inflammatory response as an organic object like a piece of wood or a thorn. If your splinter is a piece of glass, as long as it isn't from like a beaker of anthrax or something, it's not the end of the world if you can't get it out right away because the granuloma will just keep it blocked off. In fact, doctors sometimes recommend leaving small pieces of glass or metal inside of you because it's more damaging to your tissue to dig around and get it out.

But organic materials like wooden splinters, cactus spines or plant thorns are more of a problem. These little so-and-sos cause a much bigger reaction from your immune system. Woods have oils and resins in them that your cells recognize as especially dangerous, so they trigger more inflammation. They are also more likely to be covered in all sorts of harmful bacteria and fungi. That's why people get tetanus shots to protect them from Clostridium tetani, the bacterium that causes tetanus, a condition that can cause uncontrolled muscle spasms throughout your body. You might associate tetanus with like rusty nails but rust doesn't cause tetanus, it just gives the bacteria a nice home to live in. Organic matter like soil and feces can also harbour the bacteria. So if your skin is punctured by anything that's been contaminated with it, it'll make you sick. 

Another disease Sporotrichosis, more commonly called rose gardener's disease, is caused by a fungus that lives on rose thorns and can produce painful sores on your skin. In cases like these, more and more white blood cells will join the granuloma around the splinter to try to fight off the infection. And in some cases, the granuloma will get so big they have to be surgically removed. So sure, having a sliver of broken glass or a metal shaving under your skin can be incredibly painful and gross, but it turns out that splinters made of wood might be more dangerous in the long run. Every rose has its thorn, but some of them have fungi that will make you sick.

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