Thinning hair and hair loss is caused by a confluence of three facts. One of those factors is your genetics, and there's nothing you can really do about it. Unless you invent time travel or gene editing in a living person, that is, and those are pretty unlikely to say the least.
The good news is, the other two factors are things you can control. You can actively fight against your genes – or support them if your genes say you're likely to have a full head of healthy hair.
These two factors are categories: internal influences and external influences.
Internal Influences on Hair Health
Internal influences simply mean the things you put into your body that have an impact on your hair, either positively or negatively. While this can include things like drugs, both prescription and illegal, we're mostly focused on one thing right now: diet.
The things you eat have an impact on your overall health, and your overall health is expressed through a variety of systems. Poor diet manifests as everything from obesity to poor cardiovascular health to poor quality hair and nails. Thus, it's important to eat things that support your health, while minimizing the things that hurt your health when you eat them.
What should you be eating?
- Eggs. Eggs aren't going to prevent hair loss on their own, but they can contribute to resisting hair loss by supplying your body with the proteins and vitamins necessary to support hair growth and strength.
- Healthy protein. Fish in particular is great here because of the vitamins, nutrients, and omega-3s in it.
- Biotin. Another name for Vitamin V7, biotin is a critical component in hair growth and volume.
- Vitamin C. While it's not the miracle vitamin for the immune system many people think it is, it's still a potent ingredient for hair health.
- Collagen. Taking a collagen supplement, or simply eating more meat with connective tissues, helps get you collagen. Your body uses this nutrient to build and heal everything from internal injuries to skin damage to your hair.
There are plenty of other choices as well, but hey, you're in luck: we covered the topic in detail here. Go ahead and read our in-depth guide on foods to keep your hair healthy, and come back here when you want more advice beyond what you should be eating.
Now let's look at the opposite side of the coin. 
What should you avoid eating?
- Certain types of fish. Not all fish, of course; things like salmon and tuna can be very good for you. However, you want to avoid potentially contaminated fish farm-raised tuna and swordfish, because these can have high levels of mercury. Mercury poisoning can cause, among other things, hair loss.
- Processed sugar. The sugar you get from dairy and from the fruit is fine, but processed sugar like white cane sugar and high fructose corn syrup is absolutely horrible for your body. They destroy you from the inside out, slowly and insidiously, and hair loss will be one of the most visible symptoms.
- Refined grains. All-purpose flour, heavily processed grains, and refined pasta is all pretty bad for similar reasons to sugar. They induce insulin resistance throughout your body, which can eventually lead to obesity and diabetes, both of which can cause hair loss.
- Alcohol. Alcohol is a poison, albeit one that doesn't kill you right away. It dehydrates you and adds stress to your body, which leads to hair loss. Alcohol also inhibits your body's ability to absorb zinc, which is critical for hair health.
You might also consider cutting back or cutting out the caffeine. Caffeine doesn't have a direct impact on your hair, but stress does, and caffeine is often going to cause spikes and crashes in your energy levels that lead to more stress than if you aren't taking the stimulant.
External Influences on Hair Health
External influences are things you don't put in your body, but rather on your scalp. These can be anything from ambient humidity and temperature to the shampoos and conditioners you use. In fact, we'll be covering all of those bases, and more. Let's break it up into two sections: things you should do to keep your scalp happy and healthy, and things to avoid to minimize scalp damage.
What should you do to keep your scalp healthy? Other than your diet, there are a handful of things you can do, from treatments to manual stimulation of the hair follicles. Let's take a look.
- Use healthy shampoo. Some people use homemade shampoo made of eggs and oils. Other people use organic shampoos with natural ingredients. Something like a bergamot shampoo has plenty of healthy ingredients that can help you keep your hair healthy.
- Consider a medicated shampoo. If you have particular issues like psoriasis, advanced hair loss, or dry scalp skin, you can look into some medicated shampoos to help treat the issue. Keeping your hair follicles happy and healthy is the most important part of shampoo here. A common fungus, Malassezia, is also responsible for some hair loss, so an anti-fungal shampoo can help too.
- Reduce stress in your life. Yes, we know, "be less stressed" isn't very good advice. Still, if you can take some time out of your day to relax, meditate, nap, or otherwise reduce your daily stress, it can do wonders for your overall health.
- Massage your scalp. A scalp massage about once a week can help in two different ways. First, most people find it pleasant and relaxing, which helps reduce stress. Second, a scalp massage can manually stimulate hair follicles without damaging them. A scalp massage doesn't need to take long – five minutes is plenty, once a week – but it can have a surprisingly beneficial effect.
- Use a humidifier. Dehydration can damage hair, and bodily dehydration can damage a variety of systems. A humidifier helps you lose less moisture to the air, helping with both problems. Plus, it can help with other unrelated issues, like dry eye, dry skin, and dry coughs.
- Use a moisturizing conditioner. To keep your existing hair at full volume and health, you want to keep its protective layers of oils as intact as possible. Washing your hair will remove those, so you want to replace them, which is where conditioner comes in.
- Consider medical therapy. There are a few different drug treatments, like Minoxidil and Finasteride, that have been FDA approved for hair treatment. They have mixed effects for different people, though, and some side effects – like inflammation and scalp irritation – can actually worsen hair loss. Talk to a doctor about this one.
Now for the other side. What should you avoid doing to keep your scalp healthy? Some of these are easy to avoid, while others are a bit more complicated. 
Even taking some of these steps will help your overall hair health, though, and that's a good thing.
- Try not to tug. Tugging and pulling on your hair – including brushing it too much, pulling on it while drying it after a shower, and wrapping it in tight hairstyles like cornrows or tight braids – can cause damage to the hair cuticles and follicles.
- Avoid overly synthetic shampoos. While studies vary, there are a handful of different ingredients in common shampoos that might have an inhibitory effect on scalp health, especially when used too frequently or against the instructions. Organic shampoos are generally better for scalp health, while working the same for removing dirt and grime.
- Stay away from the chemical treatments. That means anything from chemical hair straightening, hair dyes, bleaches, and other harsh chemicals. All of these can damage the hair follicles, and they can damage the hair itself, making it lose its luster and volume.
- Avoid the sun. Much like how the UV radiation from the sun can damage your skin and lead to sunburn, UV rays can damage your hair and hair follicles as well. Unfortunately, you can't really rub sunscreen into your hair like shampoo and expect it to work. This is especially important if you have short hair, and you might consider actually using sunscreen on your scalp to help prevent damage. Alternatively, just wear a hat.
- Minimize heat on your hair. The three main sources of heat your hair might be exposed to are blow-drying, hot showers, and heat treatments. All of these dry out your hair and damage it beyond its ability to heal. Try to take slightly cooler showers – warm rather than hot – and if you need to use a dryer, put it on just airflow rather than heat.
Finally, one very important thing to remember: hair health is on a delay. A change you make now might not be visible in your hair for at least a month. This is why huge life events like a car accident – that lump a huge amount of stress in a short amount of time – can cause spontaneous hair loss weeks later. The damage the stress does do your body is not reflected in your hair for quite a while.
What this means is that any treatment or combination of treatments you take, any lifestyle changes you make, any dietary changes you try, they all need to be in effect for at least a month before you can start to see effects. Try to give them six months to see if they're really working, unless they have an immediate negative effect, like a shampoo causing scalp irritation. In those cases, of course, discontinue the treatment asap.
The Genetics of Hair Loss
Unfortunately, while we know that your genes play a role in hair loss as you get older, it's still not a very well understood problem. The human genome is fantastically complex, with over 20,000 genes identified. Mapping the human genome is a very recent success in science, and fully understanding is still in the beginning stages.
Once science figures out how the human genome works, we can start to identify specific genes that do specific things. This knowledge is slowing being pieced together from all angles; gene tracking helps identify everything from cancer risk to genetic disorders to autoimmune diseases. It's one of those "end goals" for medical science that is going to take decades to complete if it's ever completed at all.
So how does that play into hair loss? Well, we just don't really know. We know genetics factor into hair health and hair loss because hair loss follows the same genetic trends as other gene expressions. What we don't know is why, and what we can't know is what we can do about it.
Unfortunately, gene modification in adults, called somatic gene modification, is still a brand new technology that is very limited and very, very expensive. What's more plausible is the eventual ability to edit genes in the germline, aka the sperm and eggs, to produce gene-modified humans. Using a system like CRISPR to remove hair loss might be possible, but there are ethical concerns with gene modification in humans, and that's a whole other can of worms.
In another ten, twenty, forty years? Gene modification may be more than just a pipe dream, and a "cure" for genetic baldness may be plausible. Until such time as that happens, however, genes are just something you have to deal with. It's better to focus on the internal and external influences instead.
