A hair-like cake spreads in Vietnam—it turns out to be the lucky-charm ingredient "fat choy"

Cakes densely topped with black fuzz have started lining the display cases of Hanoi pastry shops. From a distance the item looks like nothing but a clump of shed human hair, and while people say online "it killed my appetite the moment I saw it," it has racked up hundreds of thousands of views and become a talking point among young people. The true identity is the Chinese ingredient fat choy (fa cai). This "deliberately off-putting" sweet, passed down from Thailand, moves people in the exact opposite direction of Japan's photogenic culture. Why do people go out of their way to be drawn to a look that kills the appetite? We read the distance between this new Vietnamese trend and Japan's food trends.

What is the "hair cake" - from 250,000 dong in Hanoi

According to Vietnamese reports, this “hair cake” is an impact-first confection where dried fat choy (hair moss) is sprinkled straight onto the surface of a birthday or cream cake. When the black threadlike ingredient covers the cake’s white cream, it takes on the look of a tangled mop of black hair. Its selling point is the shock, but what sits on top is edible, and while the presentation plays at being grotesque, the substance is a genuine Western-style cake.

In Hanoi, several confectioneries have started offering it, with prices per piece ranging from 250,000 to 450,000 dong depending on type (about 1,500–2,700 yen, at a rough 60 yen per 10,000 dong). The main buyers are the younger generation, and it's spreading across TikTok and several other social platforms. In video comment sections, favorable voices calling it 'unique and fun' mix with rejection like 'one look and my appetite was gone,' and that very split is what drives up view counts.

Its true identity: "fat choy"—an auspicious ingredient that invites wealth

黒い毛のような食材の正体は、髪菜(はっさい)。中国語ではファッツァイと読み、「発菜」とも書きます。ベトナムの記事はこれを乾燥海藻の一種と説明していますが、植物分類上は海藻ではなく、乾燥した土壌の表面に育つ陸生の藍藻(シアノバクテリア)の仲間です。人の黒髪が絡まったような細い糸状の見た目から、この名が付きました。中華料理では乾燥品を水で戻し、蒸したり煮たりしてスープやシチューの具に使われてきた、決して珍しくない食材です。

What's interesting is that this ingredient has long been treated as a lucky charm in China. Because the pronunciation of "fat choy" (fat cai, hair vegetable) resembles "fa cai," meaning to make a fortune, it has been favored at Lunar New Year and celebratory occasions. In other words, this trend has a double structure: an ingredient often shunned for its looks actually carries the exact opposite meaning of a "wealth-bringing food." The very gap of looking like a novelty food yet being a lucky charm is what makes it work as content.

In China, overharvesting of fat choy caused environmental damage such as desertification, so its collection has been restricted since 2000. Much of what circulates is said to be substitute material or farmed product, and this “rarity” may also be part of what makes it a talking point.

From Thailand, via Chengdu — the path this trend traveled

According to the Vietnamese article, this hair cake first caught on in Thailand and spread from there to Vietnam. Going further back, it is said to have taken off earlier in China, in Chengdu, Sichuan, in 2024. A Chinese ingredient and its lucky-charm culture, by way of Thailand's social media scene, landed with young Vietnamese as a "new, offbeat sweet"—that's the flow.

Here you can see the distinctive transmission route of Southeast Asian food trends. Whereas Japan's food booms are often imported directly from the West or from the home country of a social-media trend, Vietnam's come in by way of neighboring countries connected by land, Thailand and China. And along the way, the original context of a "lucky charm" fades, and only "how shocking it looks" gets emphasized as it spreads. The original meaning is stripped away en route, leaving only the visual shock—this is the typical way Asian social-media food goes viral now.

The opposite of “Instagrammable” — the contrarian psychology of selling on the yuck factor

Japan's food trends have long revolved around being 'Instagrammable.' Fruit sandwiches with beautiful cross-sections, vividly colored drinks, light-reflecting sheen. Beauty that makes you want to shoot it and show someone was the engine of virality. The 'hair cake' hits the exact opposite. It's true you want to photograph and share it, but the motive isn't 'because it's beautiful' — it's 'because it's gross.' The emotion being shared has shifted from admiration to surprise and disgust.

This contrarian move has a logic peculiar to social media. Beautiful things are saturated and easily buried. Discomfort and unease, on the other hand, snag hard in the brain and provoke comments and quote reactions. Even a dismissive "ugh, no way" converts into views and shares. Under an algorithm that rewards divided opinion, there are moments when offbeat looks that half the audience hates rack up bigger numbers than universally liked, photogenic ones. The hair cake is a case of exploiting that mechanism through the appearance of a single ingredient.

In Japan, too, the seeds of this "discomfort marketing" already exist. The jet-black squid-ink burger, deliberately messy-looking deli dishes, various quirky menus that went viral online. Rather than treating Vietnam's excitement as "someone else's story," it's more fruitful to read it as a leading case for Japan's food business. On another side of Vietnam's food culture,The story of a Hanoi café that dropped background music and switched to audiobooks and animeand one that puts durian, often shunned for its smell, in the starring roleA new food experience in Dak Lak, too, sits on the same line of thinking—breaking convention to create buzz.

Three takeaways Japanese food and OEM players should read

There are three takeaways that Japanese food makers and product planners can draw from this passing boom.

The first is,A perspective on designing visual 'snag'The inside of the hair cake is just an ordinary Western pastry, and its differentiation lies entirely in the look of the topping. Without greatly changing ingredients or process, there is room to spark buzz by adding a single visual jolt to an existing product. That becomes a practical weapon for small makers who want to make a product stand out without spending money.

The second isThe idea of putting the gap into words and selling itis the first. The hair cake doesn't end as mere mischief because it has a story: "looks like a novelty, but is really a wealth-bringing charm." When you can retrofit a meaningful backstory onto an outlandish appearance, a fleeting bit of buzz has a chance to roll into a product brand. Stories like an ingredient's origins, local good-fortune lore, or a devotion to production methods are exactly the assets that Japan's regional ingredients hold in abundance.

Third,A posture of picking up trends from neighboring Asia earlyThis boom traveled from China through Thailand to Vietnam. If it lands in Japan, that may be next. Watching only Western social media means missing food currents being born and raised in neighboring Asia. For makers who handle dried goods and dried ingredients, the very way an ingredient with visual impact like fat choy is used can itself be a fresh hint.

The boom's staying power, and the line not to cross

That said, this kind of "visual shock" trend never lasts long. Novelty gets stale the more it's repeated, and surprise is consumed just once. The hair cake, too, will most likely have handed the lead to some other quirky sweet a few months from now. If you're chasing it as a business, don't ride the boom itself—take home the principle of "why did people share this."

In addition, in the reporting an expert raises one concern. There's a risk that children can't tell the fat choy on the cake from real hair, and the point is that the provider needs to explain it properly. The more a product grabs attention with novelty, the more it's asked to account for "this is food, and here's what it really is." Balancing talk value with reassurance is a point that applies just as much when considering similar plans in Japan. Other Vietnamese food trends - for exampleA long-established Michelin-listed steamed rice crepe shopSet alongside the trend of tradition-rooted food steadily earning recognition, the fragility of pushing on novelty alone also comes into view.

Summary — how to turn "gross" into a business opportunity

Vietnam's hair cake is one example of moving people by being "deliberately un-beautiful" in an age saturated with the photogenic. Its true identity is fat choy, a lucky charm that invites wealth, and the gap between its meaning and its look sat at the core of the boom. If Japanese food and OEM players take something home from this, these three are practical. First, take stock of whether you can add one visual oddity to an existing product. Next, consider whether you can tie that oddity to a story of luck or origin. And add not just the West but the food trends of Thailand, China, and Vietnam to your regular observation. Not laughing off the oddity but stocking up on the transmission principle behind it—that's the step to getting ahead of the next hit.

Sources

• Dan Tri「Lạ lùng trào lưu ăn bánh phủ kín ‘tóc rối’ ở Việt Nam」
• Wikipedia "fat choy" (classification of the ingredient, its origin as a lucky charm, harvesting restrictions)