Woman’s convoluted “hair math” calculation before shower goes viral

A woman’s “hair math” dilemma has divided the internet, sparking a debate about how often women should wash their locks.

Kathrin Downs (@kathrin_downs) shared a relatable conundrum on TikTok, questioning how to schedule her hair washes throughout the week. The post quickly resonated, garnering 21,100 likes and 1.1 million views.

“The struggle is real,” she captioned the video. In it, Downs debated whether she should wash her hair immediately—meaning another wash would be needed in three days—or leave it greasy for a day to have fresh hair for an event in two days.

“So do I wash it now and wash it again later or leave it greasy for a day? Tell me I’m not alone,” she wrote, overlaying footage of herself staring flustered into the mirror.

The comment section erupted into a lively debate, with many women sharing their own hair-washing routines.

“I refer to this as ‘hair math’,” said Lena.

“Girl math” is a playful concept that gained traction on social media, especially TikTok, celebrating the unique ways women rationalize decisions—especially financial ones.

For example, it includes ideas like treating money spent in cash as “already gone,” so it doesn’t count, or thinking of returned items as “free money” to spend again.

“My bf always responds to this struggle with ‘why wouldn’t you just wash it now and then wash it again?’ and I’m like yeah and why don’t I just run a marathon every single day too,” said Whit.

“Why do people not wash their hair daily I do,” said Suzanne.

“The answer is to wash it. Dirty hair smells and I wish people would stop this,” commented another user.

“Dry shampoo solves every hair math problem,” Claire suggested.

“You mean I’m not alone with my crazy thoughts. Yeah, shampooing daily strips all the natural oils from your hair,” added Sharon.

The debate underscores an ongoing conversation about proper hair care. How often should you wash your hair? According to the hair care website Hair Code, the frequency depends on hair type, scalp health, and personal lifestyle.

For example, those with oily hair may need to wash more often, while people with dry or textured hair can space out washes to preserve moisture.

On average, they recommend people wash their hair every 2-3 days.

For those looking to extend the time between washes, the hair products retailer Wicked Roots suggests using dry shampoo, wearing protective hairstyles, and minimizing heat styling to maintain freshness.

Finally, is it possible to train your hair to get less greasy? Experts at the beauty site Byrdie say that over time, gradually washing your hair less often can help balance the scalp’s oil production. However, results vary based on individual scalp conditions.