The third and fourth stages are known as telogen and exogen, respectively. In telogen, the hair is supposed to be at "rest" until it finally detaches itself from the follicle and enters the exogen or shedding stage. Once the hair is detached from the follicle, the follicle remains inactive for about three months, after which a new cycle begins again.
The test involves plucking about 50 hairs from the head, typically at the back of the scalp, so your dermatologist can look at them under a microscope and determine how much of the hair is in the resting, growth, and fall-out phases. Next, a vial of blood is sent to a lab to check hormone and nutrient levels ($100 and up, depending on insurance). If low levels of iron, or high levels of male hormones, like androgens, are contributing to your hair loss, for example, both can be treated through oral supplements or medication.
Instead, you may want to add vitamin D (about $15) to your shopping cart. A vitamin D deficiency can exacerbate hair thinning and make it almost impossible for any over-the-counter product to reverse hair loss, says Dhaval Bhanusali, a dermatologist in New York City, who recommends taking 5,000 international units of D3 a day (and it’s generally beneficial for bone health in women over 40). “There’s also a link between low iron and zinc levels and temporary hair shedding, called [telogen] effluvium,” says Rogers.
DR. WRIGHT: If stomach acid is low, protein isn’t efficiently digested – and hair and nails are made up of… protein! If we are deficient in protein, our bodies know that we can live without hair or nail proteins, but we can’t survive without heart muscle proteins or other important body proteins. So if we are short in supply of protein, the hair or nails are the first to go.
Other causes for hair loss or hair thinning can be stress, illness, poor diet, hormone imbalance or your body going into shock. Certain diseases and intensive medical treatment such as chemotherapy are also likely to result in hair loss, but it is best to consult your GP if you go bald at an alarmingly fast rate, especially if you have no family history of male pattern baldness.
2. Volumizing shampoos and treatments. Typically, these work by depositing ingredients, like wheat protein and keratin, that adhere to the hair shaft to a) thicken it and b) create spaces between hairs so you look like you have more of it. Try Kiehl’s Rice & Wheat Volumizing Shampoo ($18) with hydrolyzed wheat protein; Rogers likes Redken Cerafill Defy Shampoo and Conditioner ($20 each) with ceramides that bulk up hair.
People have between 100,000 and 150,000 hairs on their head. The number of strands normally lost in a day varies but on average is 100.[8] In order to maintain a normal volume, hair must be replaced at the same rate at which it is lost. The first signs of hair thinning that people will often notice are more hairs than usual left in the hairbrush after brushing or in the basin after shampooing. Styling can also reveal areas of thinning, such as a wider parting or a thinning crown.[citation needed] 

There is no hard and fast answer. With Regaine Extra Strength results may be seen after 8 weeks. Clinical studies have shown that for Regaine Regular Strength or Regaine Gel for men regrowth can occur as early as 16 weeks. But remember that everyone is different so you need to be patient. Studies suggest that Regaine should be tried for 6-12 months before deciding whether to continue.
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