In South Korea, it's a popular belief that one way to get one's hair and nails to grow faster is to think naughty thoughts. But is that really the case?

Actually, the answer is no. There is no scientific evidence that having erotic thoughts directly makes hair grow faster. Hair growth is primarily regulated by genetics, hormones, blood circulation and overall health, not by thoughts or emotions alone.

What exactly is critical for their growth?

Since hair and nails constantly regenerate, they require a steady supply of keratin, water, fats and minerals. Nutrient deficiencies can weaken hair structure, leading to slow growth and increased breakage. For example, iron and zinc deficiencies are linked to both hair loss and brittle nails. Different levels of nutrients lead to the varying speeds of hair and nail growth between individuals.

Genetics play the most significant role in hair and nail growth, as growth rates tend to be consistent among family members. Identical twins often have similar nail growth speeds.

Age plays a key role too. Young people experience faster hair and nail growth. As metabolism and cell division slow with age, growth rates decrease.

Hormones and nutrition are important too, as pregnancy often accelerates hair and nail growth, while menopause and high cortisol levels (stress hormones) can slow it down. A well-balanced diet rich in essential nutrients is crucial for maintaining strong, healthy hair and nails.

In fact, several scientific studies have explored the relationship between stress and hair loss.

Studies have shown that high levels of cortisol, the stress hormone, can disrupt the hair growth cycle, slowing down growth rather than accelerating it. That is, when stressed, the body increases the production of cortisol. If this occurs repeatedly, the capillaries constrict, preventing hair follicles from receiving proper nutrients. As a result, hair growth becomes difficult due to nutrient deficiency.

So if stress is reduced by pleasurable thoughts, that could help prevent stress-related hair loss, but it won’t suddenly make hair grow faster.

Both hair and nails are primarily composed of keratin. Their growth is supported by the extracellular matrix beneath the skin, where cell division patterns determine their rate of growth.

Fingernails form from the nail matrix, a layer beneath the skin. As new cells form, older cells are pushed forward, emerging as visible nail growth. The nail plate — the flat, pink part of the nail — moves outward as new cells continue to generate.

Hair, on the other hand, grows from hair follicles embedded in the skin. The hair root is housed in a small sac known as a follicle, which is connected to nerves — this is why plucking a hair can be painful. Follicles also contain sebaceous glands that lubricate the hair and tiny muscles that cause goosebumps when exposed to cold.

At the base of each follicle is the hair bulb, which houses the dermal papilla — a structure responsible for delivering proteins, ribonucleic acid and other molecules to cells in the follicle. This supply fuels and stimulates the cells to divide and multiply.

Unlike nails, which grow continuously, hair grows in cycles.

Scientists have identified four key stages of hair growth: Anagen, which is the growth stage, lasts 2 to 8 years, during which hair actively grows. Then it goes through catagen, a transitional phase that lasts about 2 weeks, during which growth slows. The third stage is telogen, a resting phase, which lasts 2 to 3 months, when hair remains dormant. The last stage is exogen, a shedding phase, when old hair falls out, making way for new hair growth.

Throughout a person’s lifetime, each follicle repeats this cycle 10 to 30 times. If all follicles synchronized their growth cycles, we would experience periodic baldness. Fortunately, at any given time, about 90 percent of scalp hairs are in the anagen phase, ensuring continuous hair coverage.

On average, people shed 100 to 150 hairs daily, but since the human scalp contains around 100,000 hairs, this loss goes largely unnoticed.

The answer is yes. On average, human hair grows about 1 centimeter per month, while fingernails grow just over 3 millimeters per month. If left uncut, they can reach extraordinary lengths.

For example, Alia Nasirova, dubbed the “Rapunzel of Ukraine,” holds the world record for the longest hair at 257.33 cm — far surpassing her own height of 165 cm. Even more astonishing is the record for the longest nails: 1,306.58 cm, held by American Diana Armstrong.

This article is part of a series delving into trends in health and well-being in South Korea, putting popular health hacks to the test as well as introducing new developments in health care and services. -- Ed.