Several nutrient deficiencies can cause both hair loss and dry skin, but the most common culprits are iron, zinc, biotin (vitamin B7), vitamin D, and vitamin A. These nutrients each play distinct roles in keeping hair follicles cycling normally and maintaining the skin’s moisture barrier. Because the symptoms overlap so much, pinpointing the exact deficiency usually requires blood work rather than guesswork.
Iron: The Most Common Nutritional Cause
Low iron is one of the most frequently identified nutritional triggers for hair shedding, particularly in women. When your body’s iron stores drop, it prioritizes essential functions like oxygen transport over less critical ones like hair growth. The result is telogen effluvium, a condition where large numbers of hair follicles shift into their resting phase at the same time, leading to diffuse thinning and increased shedding weeks later.
The key measurement is serum ferritin, which reflects your body’s stored iron rather than the iron circulating in your blood at any given moment. Research published in Clinical, Cosmetic and Investigational Dermatology found that ferritin levels below about 24.5 ng/mL were a useful threshold for identifying people at risk for this type of hair loss. At levels below 20 ng/mL, the association became even stronger. You can have ferritin low enough to thin your hair without being formally diagnosed as anemic, which is why standard blood counts sometimes miss it.
Iron deficiency also affects the skin. Without adequate iron, cell turnover slows and the skin can become pale, dry, and more prone to cracking, especially around the corners of the mouth.
Zinc: Follicle Growth and Skin Repair
Zinc is involved in cell division throughout the body, and hair follicles are among the fastest-dividing cells you have. When zinc is low, hair follicles shrink, the hair shaft becomes brittle and poorly formed, and shedding increases. Animal studies show that zinc depletion directly causes telogen effluvium and abnormal hair fiber production.
On the skin side, zinc helps maintain the barrier that keeps moisture in and irritants out. It promotes the normal maturation of skin cells as they move from deeper layers to the surface. Without enough zinc, this process stalls, leading to dry, flaky patches and a condition called parakeratosis, where skin cells reach the surface before they’re fully developed. Zinc also plays a direct role in wound healing: when skin cells are damaged, the zinc they release triggers a signaling pathway that promotes repair.
The daily value for zinc is 11 mg. People at higher risk for deficiency include vegetarians (plant-based zinc is harder to absorb), people with digestive conditions like Crohn’s disease, and heavy alcohol users. One challenge with testing is that serum zinc levels can appear normal even when your body’s functional zinc stores are depleted, so symptoms sometimes show up before blood tests catch the problem.
Biotin (Vitamin B7): The “Skin and Hair” Vitamin
Biotin deficiency produces a recognizable pattern: hair loss paired with a scaly, red rash concentrated around the eyes, nose, and mouth. Some dermatologists call this characteristic pattern the “biotin-deficient face.” The skin changes resemble seborrheic dermatitis, with greasy-looking flakes despite underlying dryness.
True biotin deficiency is uncommon in people eating a varied diet because the daily requirement is small (30 mcg) and biotin is found in many foods. It’s most often seen in people taking certain anti-seizure medications, those on long-term antibiotics that disrupt gut bacteria, people who consume large amounts of raw egg whites (which contain a protein that blocks biotin absorption), and pregnant women, whose biotin needs increase.
Despite biotin’s enormous popularity as a supplement, lab studies have shown that adding biotin to human hair follicle cells doesn’t actually change how they grow or divide. Supplementation helps when there’s a genuine deficiency, but taking extra biotin when your levels are already normal is unlikely to improve hair or skin.
Vitamin D: Hair Cycle Regulation
Vitamin D receptors are concentrated in hair follicles, particularly during the transition phases of the hair growth cycle. These receptors help signal follicles to begin a new growth phase after the old hair sheds. When vitamin D signaling is disrupted, follicles can fail to restart their growth cycle altogether. Animal research has confirmed that without functioning vitamin D receptors in skin cells, hair follicles lose the ability to initiate new growth after the first natural cycle completes.
For skin, vitamin D regulates how quickly surface cells multiply and how they mature. It slows excessive proliferation while encouraging proper differentiation, the process by which new skin cells develop into the tough, water-resistant barrier layer. Low vitamin D can leave skin dry, rough, and slower to heal.
Vitamin D deficiency is widespread. People who live at northern latitudes, spend limited time outdoors, have darker skin, or are overweight are all at higher risk. Because vitamin D is fat-soluble and stored in body tissue, levels change slowly, and supplementation typically takes several weeks to produce noticeable effects.
Vitamin A: Too Little or Too Much
Vitamin A is unusual because both deficiency and excess can cause hair and skin problems. Too little vitamin A disrupts the normal turnover of skin cells, a process called keratinization. The clinical signs include generalized xerosis (widespread dry, scaly skin), rough bumps around hair follicles, and sparse, dry hair. A case report in Clinical Case Reports documented complete resolution of severe full-body dryness after just one week of vitamin A treatment, confirming the deficiency as the cause.
On the other hand, taking too much vitamin A, usually through high-dose supplements or medications derived from vitamin A, can also trigger hair shedding. This makes vitamin A a nutrient where balance matters more than simply “getting enough.” Deficiency is more common in developing countries and in people with fat malabsorption conditions, since vitamin A requires dietary fat for proper absorption.
Essential Fatty Acids: The Moisture Barrier
While not vitamins in the traditional sense, omega-3 and omega-6 fatty acids are essential nutrients your body cannot make on its own, and they play a direct role in skin hydration. These fats are built into the lipid layers between skin cells, forming the barrier that prevents water from evaporating through the skin surface. When essential fatty acid levels are low, this barrier weakens and transepidermal water loss increases, leaving skin visibly dry and irritated.
Clinical studies have shown that people with the lowest blood levels of certain omega-6 metabolites have the most severe barrier dysfunction, and that supplementation can reduce water loss measurably in these individuals. People whose baseline levels are already adequate see less benefit, which suggests the effect is about correcting a deficiency rather than enhancing normal function. Fatty acid deficiency can also leave hair dull and brittle, though the research on skin effects is stronger than the evidence for hair specifically.
How Deficiencies Are Diagnosed
Because so many deficiencies produce similar hair and skin symptoms, diagnosis relies on blood work rather than appearance alone. Dermatologists typically start by looking at your risk factors: your diet, any digestive conditions, medications, menstrual history (heavy periods increase iron loss), and whether you’ve had weight-loss surgery or follow a restrictive diet.
If risk factors are present, the standard workup includes iron studies with serum ferritin, serum zinc, vitamin D levels, and sometimes biotin or vitamin A. Ferritin is particularly important because it can be low enough to cause hair shedding while other iron markers still look normal. Zinc testing has its own limitation: functional deficiency can exist even when serum zinc levels fall within the reference range, so clinical judgment matters alongside the numbers.
When no clear risk factors exist, routine nutrient panels for hair loss aren’t necessarily recommended, since the yield is low. But for anyone with both hair loss and dry skin occurring together, the combination itself is a meaningful clue that a nutritional factor may be involved, and testing becomes more worthwhile.