Splinters are the pits, but usually, they're no big deal — they are the most minor of the minor afflictions that can be easily tweezed away. Occasionally, however, they can become dangerous. Even fatal. So should a splinter lodge itself under the skin, it's always a good idea to remove it as quickly as possible.
Before we all lose our heads, though, it's worth noting that death by splinter is nearly never fatal in these modern times. While it may have been a legitimate concern in, say, 1912 — when an eleven-year-old boy named Frederick Henry Booth died from a splinter he got in his hand while playing with a wooden hoop — it's not something to get worked up about in 2016. Just get the interloper out from under your skin, clean the affected area and you can move on with your day.
But while the splinter-imposed risks to one's health and lifespan are slim, they do exist and merit mention. According to HowStuffWorks, splinters vary in severity based on what they're made of, where they're stuck and how big they are. Finished wood may be coated in chemicals that inflame the skin, while certain other splinters may introduce bacteria into the body or bloodstream. HowStuffWorks cites tetanus, a condition that develops when bacteria that reside in animal waste and soil infiltrate the body, as one such danger.
Tetanus is what ultimately killed young Mr. Booth.
According to HowStuffWorks, a splinter from a plant — like a thorn — may have toxic effects on the body, and any splinter that works its way into "vital organs or blood vessels" could pose a problem. These are probably going to be tough to extract with standard tweezers and may require the eye of a medical professional.
In general, though, there's no use agonizing over a splinter — remove it if possible, and call a doctor if it's causing a lot of pain, you can't get it out, it's deep under the skin, it becomes infected or it causes a fever. If left in place, a splinter can eventually cause infection, but the likelihood that it will be the death of you is very low.