Many tips circulate regarding hair growth: onion juice, scalp massage, biotin, apple cider vinegar. What often gets overlooked is the question of what is actually supported by studies – and what is more based on plausibility or tradition. We will take a detailed look at exactly that here.
The hair cycle explained simply: Why hair grows at all
Each individual hair on your head goes through a cycle of three phases independently of the others: the anagen phase (active growth), the catagen phase (short transitional phase), and the telogen phase (resting phase, at the end of which the hair falls out). At any given time, about 85–90% of your scalp hair is in the anagen phase, while the rest is resting or about to fall out.
Crucially: Your hair grows in this active phase at a fairly constant rate of about 0.3 to 0.5 mm per day – that is approximately 1 to 1.5 cm per month. This rate is similar among most people and largely genetically determined.
What varies greatly from person to person, however, is the duration of the anagen phase. It can last between two and six years. This very difference is often overlooked in many guides on hair growth: The lever that research is most familiar with for everyday life is not the growth rate itself, but how long a hair remains in this active phase before it transitions into the resting phase. The longer the anagen phase, the longer the hair will grow – not because it grows faster, but because it has more time to do so. (An exception is made for medical agents such as minoxidil or – in the case of hereditary hair loss – finasteride, which specifically intervene in the hair cycle; more on this in the article on hereditary hair loss.)
Can hair growth really be "accelerated"?
In short: The daily rate of 0.3 to 0.5 mm cannot be reliably increased by any method known today. However, what can be influenced is, whether your hair goes through a complete, long anagen phase undisturbed – or whether external factors push it prematurely into the resting phase.
This is the actually relevant difference. So if you are looking for something that "accelerates" your hair growth, the better question is: What prevents your hair from reaching its full growth potential? And there are indeed solid answers to that.
A look at the studies shows which factors actually make a difference – and which are rather overestimated.
Promoting Hair Growth: What Studies Really Help
Nutrient Supply and Hair Growth: What Helps with a Deficiency
That a well-nourished body is an important prerequisite for healthy hair growth is no surprise. What is more interesting is how exactly the evidence looks here. Scientific reviews show: Deficiencies in Vitamin B, Vitamin D, Iron and Zinc are associated with an increased risk of hair growth disorders, and correcting these deficiencies can support hair growth.
Zinc and Selenium contribute to the maintenance of normal hair. Iron is particularly well studied: Women with non-hereditary hair loss have, on average, significantly lower ferritin levels in studies than women without hair loss.
The important addition here: These effects are particularly evident where there is actually a deficiency. Those who are already well-nourished benefit significantly less from additional supplementation.
The biotin-myth. Biotin is often marketed as a nutrient for hair growth – however, the research on this is thinner than its popularity suggests. A recent systematic review found: Biotin alone showed no consistent effect on objectively measurable hair growth. Where improvements occurred, it almost always happened in combination with other active ingredients – and could not be clearly attributed to biotin. A relevant biotin deficiency is also rare with a balanced diet. This does not mean that biotin is useless – but its role as a sole hair booster does not hold up against current research.
Caffeine and scalp massage: Promising, but not yet conclusively proven
Caffeine. Topically applied caffeine showed consistently positive effects on hair growth and loss in a review of nine clinical studies with a total of 684 participants throughout. The catch: The methodological quality of most studies is rather low – small sample sizes, often without placebo control. Promising, but not yet at the level of hard evidence.
In addition to topical agents, mechanical approaches have also been investigated.
Scalp massage. A survey of over 300 individuals with self-perceived androgenetic alopecia showed: After an average of about 7 months of regular massage routine, nearly 69% reported a stabilization or visible regrowth of hair. Also here applies: a self-disclosure survey is not a controlled study, but the mechanism – better blood circulation, better nutrient supply to the hair root – is plausible.
Home remedies for hair growth in fact check
Here it is worth taking a closer look, as most guides lump home remedies and their effectiveness together without differentiating what they were actually studied for.
Onion juice is the most cited example. The underlying study is indeed impressive: with twice daily application, around 87% of the treated individuals showed new hair growth , after six weeks compared to only 13% in a water control group. What is missing in most guides: This study was conducted on people with alopecia areata – an autoimmune disease where the body's own defense system attacks the hair follicles.This is a different mechanism than hereditary hair loss or generally slow hair growth. The statement "onion juice helps against hair loss" is therefore clearly too general.
Rosemary oil is the positive surprise among plant oils: A randomized 6-month study found an increase in hair count comparable to 2% minoxidil. This is a single study result that does not automatically make rosemary oil an equivalent alternative to the medication – but it is unusually well documented for a herbal remedy.
Apple cider vinegar, green tea, and others. remain in the realm of plausibility: Their antioxidant and pH-regulating properties are known, but controlled studies specifically on hair growth are still largely lacking.
What actively slows down hair growth – and what you can control
Can stress affect hair growth?
The connection between stress and hair loss is not just a common saying, but well-researched. Psychological stress activates the stress axis and leads to the release of Cortisol, which prematurely ends the anagen phase and pushes the hair into an earlier catagen phase. High cortisol levels also reduce the formation of important structural proteins in the scalp by up to 40%. The effect is real – and one of the few factors where stress reduction actually represents a direct biological lever, not just an indirect feel-good effect.
Smoking and Hair Growth: What Studies Show
The data is now very clear: smokers have a significantly higher risk of developing androgenetic alopecia (hereditary hair loss), than non-smokers – the risk increases further with the number of cigarettes smoked per day. Smoking likely negatively affects hair follicles through impaired blood circulation, oxidative stress, and hormonal effects .
What role do sleep, nutrition, and body weight play?
A large meta-analysis on risk factors for androgenetic alopecia found significant correlations between the progression of hair loss and poor sleep quality, alcohol consumption, and overweight. This underscores that hair growth is not an isolated issue, but is closely related to your overall health.
Hair breakage due to heat and aggressive care
Frequent blow-drying and straightening at high temperatures, as well as aggressive, drying ingredients, damage the hair's cuticle. This does not lead to less hair growth at the root, but to more hair breakage in the lengths – making your hair overall visibly longer at a slower rate, even if it grows normally at the root.
When lifestyle measures reach their limits: The different forms of hair loss
Not every hair loss responds the same way to the aforementioned adjustments.Roughly, research distinguishes several forms: diffuse hair loss (usually temporary, triggered by stress, malnutrition, or hormonal changes), circular hair loss (an autoimmune disease where the immune system attacks its own hair follicles), and hereditary hair loss, medically referred to as androgenetic alopecia. The first two forms are usually time-limited and can be significantly improved by addressing the cause – such as a balanced nutrient intake or less stress –
In contrast, the hereditary form is different. All the aforementioned adjustments help to fully utilize the genetic potential of your hair, but they cannot compensate for a hereditary sensitivity of the hair root to hormones.In androgenetic alopecia, hair follicles react hypersensitively to dihydrotestosterone (DHT), a breakdown product of testosterone. This leads to a further shortening of the anagen phase with each cycle, and the follicles increasingly atrophy.
The patented HSF technology targets the consequences of this mechanism, which is also used in the Hair Restoration Serum . It was developed as part of research into cellular regeneration processes and is based on findings related to the hypoxia-inducible factor (HIF) – that signaling pathway whose fundamental research was awarded the Nobel Prize in Physiology or Medicine in 2019. In a clinical study, 80% of the 20 participants with hereditary hair loss showed reduced hair loss after six months.
If you suspect that there is more than "normal" hair loss behind your situation, it is also worth taking a closer look at the mechanisms and what actually helps – you can find more about this in our article on hereditary hair loss.
Conclusion: Myth vs.Fact
| Myth | What research shows |
| “Biotin is THE hair booster" | Benefits have so far been proven primarily in cases of documented deficiency |
| “Onion juice makes hair grow faster" |
So far only studied for alopecia areata |
| “Home remedies are an equivalent alternative to everything else" |
Research varies greatly – rosemary oil comparatively well studied, most others hardly at all |
The growth rate of your hair cannot be increased according to the current state of research – this applies regardless of whether your hair growth is currently normal or affected by hair loss.What you can influence is whether your hair goes through its anagen phase as undisturbed as possible: through good nutrient supply, less stress, and gentle care. If there is additionally a genetically conditioned cause behind it, that alone is often not enough – a more targeted approach is needed here, which directly addresses the shortened anagen phase and the hair loss itself, as is the case with the HSF technology. The actually relevant question is therefore less "How can I make my hair grow faster?" but "How do I tap into the growth potential that my hair actually has?" – and depending on the cause, different answers are required.
