Hair grows an average of 0.5 to 1.7 centimeters per month, which works out to roughly a quarter inch to just over half an inch. That’s slow enough that it can feel like nothing is happening, especially if breakage, shedding, or a health issue is offsetting your growth. The good news is that most causes of stalled hair growth are identifiable and reversible.
How Hair Growth Actually Works
Every hair on your head cycles through three phases independently. The growth phase (anagen) lasts several years and is when the follicle actively pushes out new hair. A short transition phase follows, lasting a few weeks, during which the follicle shrinks and the hair detaches from its blood supply. Then comes the resting phase (telogen), where growth stops entirely. About 10 to 15 percent of your scalp hairs are in this resting phase at any given time, and they can stay dormant for up to a year before falling out and being replaced.
This means your hair is always growing, resting, and shedding simultaneously. Losing 50 to 100 hairs a day is completely normal. What feels like hair that “won’t grow” is usually one of two things: something is pushing too many follicles into the resting phase at once, or new growth is breaking off before it reaches a noticeable length.
Stress-Related Shedding
One of the most common reasons hair suddenly seems to stop growing is a condition called telogen effluvium. A major stressor, whether physical or emotional, shocks a large number of follicles out of the growth phase and into the resting phase all at once. The tricky part is the delay: shedding typically starts two to three months after the triggering event, so by the time you notice thinning, you may not connect it to the original cause.
Common triggers include severe illness or high fever, major surgery, significant emotional stress, crash dieting, low protein intake, iron deficiency, and the hormonal shift after giving birth. The shedding itself usually lasts three to six months, and once the underlying cause is addressed, hair regrows on its own within six to eight months without any treatment. If you’ve recently been through something physically or emotionally intense, this is a likely explanation.
Hormonal Imbalances
Thyroid problems are a well-known but often overlooked cause of sluggish hair growth. When your thyroid is underactive, it slows the division of cells in the hair follicle, pushing hairs into the resting phase prematurely and delaying the start of new growth cycles. This creates a pattern of gradual, diffuse thinning rather than bald patches. Proper thyroid signaling does the opposite: it extends the growth phase, promotes cell activity in the follicle, and delays the regression that ends each growth cycle.
Androgens, the group of hormones that includes testosterone, also play a significant role. A potent form of testosterone called DHT can shrink hair follicles on the scalp over time, producing thinner, shorter hairs with each cycle until the follicle essentially stops producing visible hair. This is the mechanism behind pattern hair loss in both men and women. Estrogen, by contrast, generally supports hair growth, which is why many people notice thicker hair during pregnancy (when estrogen is high) and significant shedding afterward (when it drops sharply).
Nutritional Deficiencies
Your hair follicles are among the fastest-dividing cells in the body, which makes them sensitive to nutritional shortfalls. Iron deficiency is one of the most common culprits, particularly in women with heavy periods or people on restrictive diets. Low iron limits the oxygen supply to follicles and can trigger excessive shedding. Protein deficiency has a similar effect: when your body doesn’t get enough protein, it conserves what it has for essential functions and deprioritizes hair production.
Zinc, biotin, vitamin D, and B vitamins all support the hair growth cycle. A deficiency in any of them can slow growth or increase shedding. If your diet is highly restrictive, or if you’ve recently lost a significant amount of weight quickly, nutritional gaps are worth investigating with a blood test.
Medications That Disrupt Growth
Several common medications can push hair follicles into the resting phase. Beta-blockers (used for blood pressure and heart conditions), retinoids (including high-dose vitamin A supplements), blood thinners, certain anti-seizure drugs, and some thyroid medications are the most frequently linked to hair shedding. Even immunizations have occasionally been associated with temporary hair loss.
The pattern looks similar to stress-related shedding: diffuse thinning that starts a few months after beginning the medication. If a medication is responsible, hair growth typically restarts after the drug is stopped or switched, though this is a conversation to have with whoever prescribed it rather than a decision to make on your own.
Scalp Conditions and Inflammation
Healthy hair needs a healthy scalp. Conditions like seborrheic dermatitis cause inflammation, flaking, and a buildup of oily, yellowish scale around the hair follicles. In more severe cases, thick scales can encase groups of hairs and bind them together. This chronic inflammation doesn’t just feel uncomfortable. It can disrupt the environment follicles need to cycle normally, contributing to thinning over time.
Psoriasis, fungal infections, and allergic reactions to hair products can cause similar problems. If your scalp is persistently itchy, flaky, red, or tender, treating the underlying condition often improves hair growth.
Breakage vs. Slow Growth
Sometimes the issue isn’t that your hair won’t grow. It’s that new growth is snapping off as fast as it appears. Heat styling, chemical treatments, tight hairstyles (ponytails, braids, extensions), and aggressive brushing all weaken the hair shaft. If your hair seems stuck at a certain length, breakage is a likely factor, especially if you notice short, uneven pieces around your hairline or part.
Protecting the hair you already have is just as important as encouraging new growth. Reducing heat exposure, avoiding styles that pull on the roots, and using a wide-tooth comb on wet hair can make a measurable difference over a few months.
What Actually Helps Hair Grow
Minoxidil, the active ingredient in products like Rogaine, is the most studied topical treatment for hair growth. It works by increasing blood flow to the follicle and extending the growth phase. Results take time: most people see no significant change at three months, with measurable improvements appearing around the six-month mark.
Rosemary oil has gained attention as a natural alternative. A clinical trial comparing rosemary oil to 2% minoxidil for pattern hair loss found that both groups had a significant increase in hair count at six months, with no meaningful difference between the two. Neither group showed improvement at three months. So if you try either option, patience is essential.
Beyond topical treatments, the most effective thing you can do is identify and address the root cause. If it’s nutritional, correct the deficiency. If it’s hormonal, get your thyroid and hormone levels checked. If it’s stress-related, the reassuring reality is that your hair will almost certainly recover on its own once the trigger passes. The hair growth cycle is slow by design, so any fix, whether medical or lifestyle-based, needs at least three to six months before you can fairly judge whether it’s working.