Researchers estimate that 10% of the U.S. population is afraid of the number 13. The fear of the number 13 even has its own name: triskaidekaphobia. Meanwhile, paraskevidekatriaphobia is the name of the specific fear of Friday the 13th, which can result in people avoiding traveling or marrying on that day.
While there is no proof that the number or date are truly unlucky, there are some theories as to why people think they are. One is tied to the last supper in which Judas, the disciple who betrayed Jesus, was the 13th person to sit at the table. Some believe the last supper itself happened on the 13th. Another theory relates to the code of Hammurabi, the Babylonian code of law of Ancient Mesopotamia where the 13th law is said to be omitted.
The number is also linked to sorcery, as witch covens traditionally had no more than 13 members. Mathematicians have long thought 12 to be a “perfect” number, which is why we use it to measure time, so the number 13 just seems odd and imperfect in comparison.
13 is also considered to be a female number as it represents the average number of a woman’s menstrual cycle in a year, and before patriarchal times, Friday the 13th was considered the day of the goddess. But as women were made to feel shame for their menstrual cycles and goddesses were abandoned as deities, the day no longer had a positive connotation.
A fear of the number 13 is mainly a western thing, as many cultures actually see the number as lucky. However, the number 4 is avoided in much of East and Southeastern Asia due to it sounding similar to the word “death” in Chinese. This fear also has its own name: Tetraphobia. In cultures where 4 is taboo, the number is even avoided around sick family members.