The Five Vitamins That Time Forgot and What They Actually Do for Your Skin

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In 1923, two biochemists at the University of California announced they had found a new vitamin and gave it the next available letter: vitamin F. Within six years, the scientific establishment changed its mind. What they had identified was not a vitamin at all – it was a fat. That reversal was just the beginning of one of nutrition science’s stranger episodes, a period in which letters F through J were handed out, debated, renamed, and in some cases quietly retired. The chaos left a gap in the alphabet that most people notice but rarely question. But the real story is not about naming conventions. Several of those so-called missing vitamins turned out to be genuinely important compounds – especially for skin health – and some of them are now having a serious moment in modern skincare. Knowing what they are and where they went matters, particularly if you care about what goes into your serums and supplements.

Why Did Scientists Skip from E Straight to K?

The lettering system for vitamins started simply enough. Researchers in the early twentieth century were hunting for the compounds that prevented specific deficiency diseases – scurvy, rickets, beriberi – and they named each new discovery with the next available letter. Vitamins A, B, C, D, and E fell into place between about 1913 and the early 1920s in reasonably logical order. After that, the system buckled under the weight of competing teams, different national naming conventions, and the messy reality that many substances initially classified as vitamins turned out to be something else entirely. The British and American research communities sometimes gave the same substance different letters, each side unaware of – or unimpressed by – the other’s work. The Germans, meanwhile, decided to name some compounds based on apparent function rather than order of discovery, which produced vitamin H (named for ‘Haut,’ the German word for skin) and vitamin K (named for ‘Koagulation’).

By the 1930s, the neat alphabetical sequence had fractured, and international committees began the slow work of standardizing names – a process that involved folding many of the later-discovered compounds into the already-established B complex under numbered designations. Letters F, G, H, I, and J were caught in this transition. Some got new names and new numbers. Some were absorbed into other categories entirely. And two of them simply never made the cut for humans. The result is the peculiar gap on the supplement shelf: vitamins A through E, then K – with five letters conspicuously absent in between.

What Is Vitamin F and Why Is It Back in Skincare?

Vitamin F is the name originally given to the essential fatty acids – specifically linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid). The term was coined in 1923 when Herbert McLean Evans and George Oswald Burr identified these compounds as necessary for normal growth in laboratory animals. Their early data was persuasive enough to warrant a vitamin designation. By 1929, however, after further research showed that the body handles these compounds more like dietary fats than like traditional vitamins, the classification was dropped from most official systems. The substances themselves did not go anywhere, though. They are still described as essential – meaning the human body cannot synthesize them and must obtain them from diet or topical application – and they are now understood to play a central role in maintaining the skin’s outer barrier.

When linoleic acid is applied to the skin, it does something worth understanding: it gets incorporated into ceramides, the lipid molecules that form the skin’s protective barrier. Ceramides account for roughly 50% of the lipids in the outermost layer of skin, and they are responsible for keeping water in and irritants out. A 2024 review in the International Journal of Cosmetic Science confirmed that ceramide levels decline measurably with age, and that topical formulations containing essential fatty acids can help restore barrier function. The full citation is available at https://onlinelibrary.wiley.com/doi/10.1111/ics.12972. This is why vitamin F – or linoleic acid – appears increasingly in serums, face oils, and barrier creams. It is also why oils naturally rich in linoleic acid, like rosehip, evening primrose, and sunflower seed, have long been popular in natural skincare. The science caught up with the intuition. Vitamin F may have been stripped of its official title a century ago, but the skincare industry has effectively reinstated it.

Is Vitamin G the Nutrient Your Skin Already Knows?

Vitamin G was the American name for what the British called B2, and what the world eventually settled on calling riboflavin. The truce happened in the 1930s, when international scientific bodies decided that riboflavin – which had been studied under at least three different names depending on which laboratory you asked – would be standardized as vitamin B2. The ‘G’ designation disappeared from the literature almost overnight, and most people today have never heard it. What many people have heard is riboflavin, even if they do not fully know what it does. It is one of those nutrients that shows up on every cereal box and multivitamin label without much fanfare or explanation. The story of vitamin G is largely the story of scientific diplomacy: two countries, one compound, and a name that had to go.

Riboflavin supports cellular energy production in every layer of the epidermis, and it functions as an antioxidant by helping neutralize the free radicals that contribute to oxidative stress and accelerated skin aging. It is also involved in collagen synthesis – not directly, but by supporting the enzymatic processes that keep collagen production running properly. Research published in PubMed Central has highlighted riboflavin’s anti-inflammatory properties and its use in skincare formulations targeting rosacea, acne, eczema, and uneven pigmentation, with the full review available at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7037471/. You will rarely see it listed by its old name on an ingredient label. But if a product lists riboflavin or vitamin B2, the forgotten vitamin G is exactly what you are getting. And it earns its place.

Why Did Vitamin H Get Named After Skin in the First Place?

The naming of vitamin H is one of the more charming stories in the history of nutrition science. In the 1930s, German biochemist Paul György was investigating a condition known as ‘egg-white injury’ – a syndrome in which rats fed large amounts of raw egg whites developed severe skin rashes, hair loss, and muscle weakness. The culprit turned out to be a protein in raw egg whites called avidin, which binds to a specific nutrient in the gut and prevents its absorption. In 1939, György isolated the compound that reversed these symptoms and named it vitamin H, drawing on the German words ‘Haar’ (hair) and ‘Haut’ (skin) to honor its protective role in those tissues. The name captured something real: the compound György had found had a demonstrable and direct connection to skin integrity, hair growth, and nail structure. It was an unusually poetic moment in a field not known for sentimentality.

Biotin – which is what vitamin H is now called – is classified as vitamin B7 and is one of the better-studied members of the B complex. It plays a central role in producing the enzyme reactions that support fatty acid synthesis, which in turn supports the skin’s natural lipid barrier. It is also essential for keratin production – keratin being the structural protein that forms the scaffold of skin cells, hair shafts, and nails. The NIH’s Office of Dietary Supplements has confirmed that biotin deficiency produces clear dermatological symptoms including skin rash and hair thinning, with their full fact sheet at https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/. Biotin supplements are widely sold with claims about hair and nail benefits, and while the evidence is strongest for people with an actual deficiency, getting adequate biotin through diet – eggs, nuts, salmon, sweet potatoes – matters for everyone who wants healthy skin and hair. The German researchers who named it for skin and hair were not wrong. They just used a name that did not survive standardization.

What Actually Happened to Vitamins I and J?

Vitamins I and J are the most anticlimactic entries in this story, which is itself part of the story. Vitamin I was identified in early research as having a role in digestion, and researchers working in the 1920s and 1930s used the designation informally for several candidate compounds. The problem was that none of these compounds ever resolved into a single, distinct, essential nutrient separate from the ones already being catalogued. As the B complex grew through the 1930s and 1940s to encompass B2, B3, B6, B7, B9, and B12, various substances that had briefly carried an ‘I’ label were absorbed into that expanding list under their B-designations. The letter I was never officially assigned to any vitamin that survived standardization. It sat empty in the alphabet, a placeholder for a discovery that never quite arrived. The history of vitamin I is, in a sense, the history of how hard it is to prove that something is truly new – especially when you are working before mass spectrometry and before research teams in different countries could easily share data.

Vitamin J has a slightly different history. Historical accounts describe it as a substance found beneficial in guinea pig studies but not considered necessary for humans – a fairly common fate for candidate vitamins in that era, when researchers were casting a very wide experimental net. Some more recent sources have informally applied the vitamin J label to choline, an essential nutrient involved in cell membrane production and liver function. But choline has its own distinct classification and status as an essential nutrient, and the vitamin J designation never stuck in any official capacity. The honest answer is that vitamin J is a placeholder the science ultimately decided it did not need. Neither vitamin I nor vitamin J appear in any current regulatory framework, and there is nothing in modern research to suggest that is likely to change.

How Do These Forgotten Vitamins Affect Aging and Mature Skin?

This is where the practical value of all this history comes together. As skin ages, several things happen simultaneously that the nutrients from this so-called missing group directly address. Ceramide production drops with each decade, making the skin increasingly susceptible to moisture loss, irritation, and the visible thinning that comes from a compromised outer barrier – which is precisely where vitamin F (linoleic acid) becomes especially relevant, since it is a direct precursor to the ceramides the skin can no longer produce at the same rate. The skin’s natural antioxidant defenses become less efficient over time as mitochondrial function declines – which is where riboflavin’s role in neutralizing oxidative stress and supporting cellular energy production has a tangible effect. And keratin metabolism slows with age, affecting not just hair and nails but the renewal of the outermost skin layer, which is where biotin’s support of keratin pathways matters. These are not minor or marginal effects. They represent three distinct mechanisms through which the nutrients once labeled F, G, and H continue to do significant work.

For mature skin specifically, the barrier repair story is the most important one. After roughly the age of 50, the skin loses lipids – including the ceramides that linoleic acid supports – at a faster rate than they can be replenished through normal cell turnover. Dryness, sensitivity, and the appearance of fine lines that comes from chronically dehydrated tissue all follow from this process. Topical products containing linoleic acid, or oils like sunflower, rosehip, or evening primrose that are naturally rich in it, directly address this deficiency at the barrier level. They do not work overnight, and they are not substitutes for prescription-strength interventions when those are warranted. But for daily skin maintenance, especially in the 60s and beyond, ingredients that support ceramide production deserve serious attention. The 2024 ceramide research referenced earlier indicates that the skincare industry is already moving in this direction – and the compound it is increasingly turning to is one that once held the name vitamin F.

Riboflavin similarly becomes more relevant with age. Mitochondrial function declines as we get older, and riboflavin is essential to mitochondrial energy production – including in skin cells, where adequate energy supports the repair and renewal processes that slow down visibly after midlife. While applying riboflavin topically is less common than consuming it through food or supplements, ensuring adequate dietary intake through dairy, eggs, lean meats, and leafy greens keeps the cellular machinery running that skin regeneration depends on. Biotin, while unlikely to produce dramatic results in people who are not deficient, supports the fatty acid metabolism underlying barrier integrity. People eating a varied diet generally get enough through food, but very low-calorie eating patterns, gut health issues, or extended use of certain antibiotics and other medications can deplete it. For those in their 60s and 70s, it is worth checking whether diet is consistently delivering adequate amounts of all three.

FAQs

Is vitamin F the same as omega fatty acids?

Essentially yes. Vitamin F is the old name for two essential fatty acids – linoleic acid (omega-6) and alpha-linolenic acid (omega-3). The ‘vitamin’ label was dropped in the late 1920s when researchers determined these compounds function more like dietary fats than traditional vitamins. But the essential fatty acids themselves remain deeply important nutrients for both overall health and skin function. In skincare, you will find them in oils like rosehip, sunflower seed, and evening primrose, and increasingly in dedicated serums and barrier-repair formulas.

Can I get vitamin G benefits from food?

Yes, and you probably already do. Riboflavin – the compound that was briefly called vitamin G before being renamed B2 – is found in dairy products, eggs, lean meats, almonds, and leafy green vegetables. Most people eating a reasonably varied diet get enough. If you are interested in topical benefits, riboflavin does appear in some skincare formulations where it shows up as riboflavin or vitamin B2 on the ingredient list. It is not as widely used topically as linoleic acid or biotin, but the antioxidant and anti-inflammatory research behind it is solid.

Does biotin (vitamin H) really make hair grow?

Biotin supports the keratin infrastructure that underpins hair structure, and a genuine deficiency will cause hair thinning and loss that resolves with adequate intake. The popular claim that extra biotin supplements produce dramatic hair growth in people who already have sufficient levels is a different matter, and it is not well-supported by clinical evidence. The NIH notes that biotin supplement claims for hair, skin, and nails in non-deficient individuals are backed by at best a handful of case studies and small trials. Getting adequate biotin through a varied diet is the most reliable approach.

Are vitamins I and J worth looking for in skincare products?

No. Neither vitamin I nor vitamin J reached official classification as vitamins for human use. Vitamin I was never definitively assigned to a single compound, and vitamin J was found necessary for guinea pigs but not for humans. If you see these terms on a product label, treat them with healthy skepticism – they are not recognized or established skincare ingredients, and no regulatory body currently endorses their use as nutritional or topical designations.

For mature skin in particular, is vitamin F worth prioritizing?

Very much so. Vitamin F is not always listed by that name, but products containing linoleic acid, or oils like rosehip, sunflower seed, and evening primrose that are naturally high in it, deliver exactly the essential fatty acids that once held this designation. For skin experiencing dryness, reduced elasticity, or barrier sensitivity – all common concerns from the 50s onward – products rich in linoleic acid are worth prioritizing. Consistent use over weeks to months, rather than expecting immediate results, is how barrier repair ingredients perform best.

The real lesson from vitamins F through J is that the naming system for nutrients was always messier than the neat alphabetical row on a supplement bottle implies. Science does not always progress in order, and sometimes a substance gets its letter before the research is finished. What matters is the biology, and in the case of essential fatty acids, riboflavin, and biotin, the biology held up even when the names did not. Vitamin F became ceramide science. Vitamin G became B2. Vitamin H became the nutrient responsible for keeping your skin‘s structure intact. The letters were temporary. The compounds were real. And if you are looking for ways to support your skin’s barrier, antioxidant defenses, and structural proteins as you age, the forgotten vitamins have a lot to offer – you just need to look for them under their current names.