Causes of hair loss is a common but a wide topic under discussion. There can be various causes for hair loss.
I had thick curly hair during my teenage years, but I saw it thinning out and my scalp visible to the outside when I stepped into my 20s. I was worried about this and wanted to know why this is happening.
Therefore I did my own information search and found out that the following 14 causes could cause hair loss in both men and women regardless their age.
1. Hair loss due to genetics
Genetics and heredity is one of the main causes of hair loss. This is a natural condition where the hair loss is due to your genetic makeup.
This is highly common among men, but even women lose their hair due to heredity. 
Therefore there is a common belief that the genetic hair loss is inherited by a particular person from his mothers side. However, this belief is only half true.
The experts have pointed out that, if the mother or the close relatives from the mother’s side had experienced hair loss, then you have a higher probability to lose hair too. But this is not the only heredity factor which can cause hair loss  .
The recent studies and conclusions state that the genes which cause genetic hair loss can be inherited from both mother’s and father’s side.
The unfortunate news is that you cannot stop hair loss due to heredity. But you can slow down the process by various treatments such as applying a minoxidil based product.
2. Vitamin deficiency could cause hair loss
Vitamins are essential to be included in our daily diet. It is responsible for many vital functions of the body. These functions also include assisting in hair growth, in various ways.
Vitamin deficiency is another one of the causes for hair loss, which is ignored by most people. Vitamins A, B, C, D and E are all important to prevent hair loss as they are responsible for collagen production, production of red blood cells to carry oxygen, and generate new hair follicles.
The studies also state that, overdosing such vitamins through supplements, can be harmful and can also lead to hair loss. Especially vitamin A. Therefore be mindful to take the recommended amounts only.
Click here to view the recommended nutritional intake for a healthy adult by British Nutrition Foundation.
3. Sudden weight loss
You might lose weight for unintentional reasons such as stress and trauma or for an intentional reason such as a crash diet. At this point, the main focus is on weight loss due to crash diets.
When you are on a crash diet, your body will be deprived of the carbs, healthy fats and other vital vitamins. A crash diet may help you with weight loss, but it can also be a reason for hair loss, due to the reduction in overall calorie intake.
Calories are important for your body to provide energy for the cells to perform its vital functions. If there is no energy for the cells, then there is no cell growth.
Therefore if you are trying to lose weight by following a crash diet, do not restrict your calorie intake to a dangerous level. Instead, follow a balanced diet plan which will not restrict vital nutrients too much.
Such diet plans may take some time to produce results in weight loss, but it will not put your hair and other health aspects at risk.
The hair loss due to sudden calorie restrictions will be temporary and your hair will be back to normal once the required nutrition intake is taken.
4. Showering mistakes
I have emphasized before on various kinds of mistakes that we make in our shower. These mistakes can have a huge impact on our hair.
Using too much shampoo, rinsing off in hot water, showering hard water etc. could damage your hair leading to hair loss.
These mistakes may seem insignificant, so we are giving little attention to them. However, such mistakes can damage your scalp and hair follicles, causing temporary hair loss and even permanent hair loss in extreme situations.
5. Hair loss after the delivery
According to the scientists and the hair experts, at any given point of time approximately 90% of your hair grows while the remaining 10% goes into the resting phase. Approximately in two to three months, this resting hair will fall out, and new hair will grow again in its place. This is the normal hair cycle.
The most common effect on hair during the pregnancy period is that more hair remains on the growth phase. As a result a pregnant mother would have a fully grown luxurious hair. 
The hair loss of a pregnant mother is more likely to occur after 3 to 4 months following the delivery.
During the pregnancy period, the level of hormones seems to increase. Especially estrogen. This rise in hormones will keep the hair at the growing phase without going to the resting phase.
However, after the delivery, this condition would return back to normal.
As a result, more of the hair which was at the growing phase due to the rise in estrogen will move to the resting stage and fall off.
6. Hair styling techniques could cause hair loss
The products and the techniques that you use to style your hair, can damage your hair. Such damaged hair is more vulnerable and prone to break easily.
Hair gel and hairspray – Over using hair gel and hairspray can dry your hair strands. This is due to the alcohol content in your hair product. The dry hair is weak, vulnerable and breaks easily.
Further, make sure that hair gel and spray does not touch the scalp. They can clog the hair follicles, making it hard for the hair to absorb the required nutrition and grow.
Flat irons and hair dryers – When you use flat irons and hair dryers, make sure to adjust the heat to medium or less. Too much heat can damage and weaken your hair.
If you are using flat irons, curling irons and hair dryers, make sure not to use them every day. Limit the use of such products to three days a week max.
It’s better to allow your hair to air dry naturally, rather than using a hair dryer. However , due to our busy schedule, waiting for a longer period of time is not an option. But at least, wait until your hair is partially dry, to use the hair dryer.
Hair styles – Do not use hairstyles like cornrows, braids and ponytails which pulls the hair hard, especially when the hair is wet. Such hairstyles can damage the hair roots, leading to hair loss
7. Anabolic steroids
Anabolic steroids is a type of drug which can mimic several natural hormones in our body. Steroids will control and regulate how the body and the muscles develop.
Anabolic steroids have various side effects. Hair loss is one of such side effects of using anabolic steroids.
Steroids will increase the production of Dihydrotestosterone (DHT) hormone. DHT is one of the main hormones which can cause baldness.
According to the scientists, DHT will attach to the hair follicles and over the time such follicles will degrade. Also, DHT will shrink the size of the hair follicles, making the new hair thin and weak.  
Further, the research information indicates that use of anabolic steroids over a long period of time can kill the hair follicles causing no hair growth which can lead to baldness. This can be permanent.
So it is better to stay away from anabolic steroids.
Certain types of medications can manipulate how our body works. Such medications are one of the main reasons for hair loss, and hair thinning.
Medication will interfere with the hair growth cycle. Generally, the medication will induce more hair to go into the resting phase. This will cause hair to fall prematurely. 
According to the experts, the hair loss due to medication occurs within 2 to 4 months of taking the relevant medicine.
The drugs that can lead to hair loss are antidepressants, antibiotics, anti clotting drugs, Blood pressure medications, cholesterol lowering medicine, birth controlling pills etc.
The hair loss due to medication is considered to be temporary, and the hair growth will return back to normal within several months of stopping the respective medication.
Do not stop your medication just because it causes hair loss. Consult your doctor before making such a decision.
9. Anemia causes hair loss
Anemia is a medical condition that occurs when your body is deprived of iron, therefore the level of red blood cells and haemoglobin will also be minimum.
There are several types of anemia. Such types are sickle cell anemia (happens due to genetics), iron deficiency anemia, vitamin deficiency anemia etc.
Red blood cells and haemoglobin are responsible for carrying oxygen through our body. Therefore, low levels of red blood cells and haemoglobin leads to decreased levels of oxygen in our body.
Oxygen is important to keep the cells in our body healthy, thereby keeping the skin and the hair healthy. Therefore lack of iron can lead to hair loss. 
According to the experts, the deficiency in iron will not damage the hair follicles completely. Therefore there is some hope for hair to regrow after losing hair due to anemia.
However if you feel like your body is lacking iron and other nutrition, seek the advice of a doctor. The doctor will recommend blood tests and necessary medication depending on your condition.
10. Protein deficiency
Protein is crucial for strong and healthy body tissues, including the hair.
Our hair is also made up of a protein called keratin. Lack of protein can lead to weaker and thin hair, which are more vulnerable and prone to break. 
The hair loss from protein deficiency will be temporary and the hair will grow back and be strong once adequate level of protein is taken.
11. Thyroid gland problems and Hormone imbalances
An underactive or overactive thyroid gland can create hormone imbalances. Such imbalances can affect the hair cycle. 
According to the medical experts, mild thyroxine imbalances will not cause hair thinning. However, if the condition is not treated and gets severe, then it may cause hair loss.
If you feel that you have a hormone imbalance, consult your doctor. The doctor may recommend blood tests depending on your condition, to check for hormone imbalances.
Hair loss due to hormone imbalances will be temporary. With proper medication and treatment, noticeable hair growth may be seen. But it will take several months of continuous treatment, to see the results.
You may have stress due to various reasons. It can be physical stress, mental stress or any other kind. The bad news is that all these stress types can lead to hair loss.
According to the experts, stress can affect the hormone balance in our body. Which will induce more hair to go to the resting phase than usual, affecting the growth pattern of the hair follicles. This will thin out the hair on certain spots in your head.
Hair loss due to the stress is considered to be temporary, and the hair growth will return back to normal within several months, after resolving the stress.
13. Pollution and other environmental conditions
The toxin gases and dust particles in the air can affect the hair negatively. The air pollution may be man made or natural, but both of these can cause hair loss.
The polluted air particles with dust can block the pores in your head and the pollution can increase the free radicals (unstable electrons) in our body which could damage the cell structure thereby weakening the hair.
The hair loss from pollution is temporary, however with age our body loses the ability to fight against the damage caused by pollution.
Add more vitamin C and vitamin E in your diet, to help your body to fight against the damage caused by pollution.
Dandruff is a type of fungus that grows on our head. According to some experts, dandruff does not lead to hair loss directly. However, dandruff will be itchy and the constant scratching of the hair will damage the hair roots, causing hair loss.
However there is another theory which is not clearly proven. That is, being a fungus, the dandruff needs nutrition to survive. Such nutrition will be taken from the scalp and the hair making the hair weaker. This can cause hair to fall prematurely.
Hair loss from dandruff is considered to be temporary. However, untreated conditions may lead to permanent damages. Shower daily and use dandruff shampoo at least 3 times a week to get rid of dandruff.