The ink might be ballpoint, gel, or rollerball. The mechanism might be click top, twist action, or cap. It might have a stylus, pocket clip, ergonomic shape, or multiple inks. The defining characteristic of an antimicrobial pen is a special additive that suppresses the growth of microbes. This additive prevents fungi, bacteria, yeasts, and algae from growing and won’t wear off through the years. It’s incorporated into the barrel material and often additional parts of the pen including the nose cone, click top, and pocket clip.