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The thickness of your hair depends on how exactly it grows from your head. Most of what causes thick hair is beyond your control, although you can make the most of what you have with strengthening and volumizing tricks. If your hair's thickness changes unexpectedly, visit a doctor to rule out chronic conditions.
Genetics
Your genetics determine the thickness of your hair. Look to your parents and grandparents for clues to your hair's texture. Since this information is encoded in your DNA, you can't do too much to change it, but you can manage what nature gave you by knowing what to expect.
Follicles
Hair follicles are little pockets all over your scalp that grow hair. Large follicles produce thick hair. Small follicles produce thin hair. It really is that simple, but your head may have a mix of follicle sizes. This is true for straight, wavy or curly hair. While oblong follicles produce waves and curls -- that get progressively tighter as follicles become more elongated -- the smaller oblongs produce fine, curly hair and the bigger oblongs produce thick, curly hair.
Pregnancy
Pregnancy can temporarily affect the thickness of your hair. Your hormones are all over the map right now. An increase in androgen can lead to thick hair's growing on different parts of the body -- including a few you might not want. In many instances, when you return to a pre-pregnancy hormonal level, your thick hair will fall out or stop growing.
Protein
If you wish you had the look of thick hair, but feel a bit limp, you can bolster the look of thickness with a protein pack. These hair masks do not actually make your hair thicker, but they can give hair resilience, bounce, volume and strength that helps it look thicker. They're also good for hair that is thick and brittle. Protein packs can help African-American hair that stresses at the bends in tight coils, but it still won't really make your hair thicker. Additionally, overuse can make anyone's hair brittle.
Pathology
If your hair becomes thicker or if you start growing thick hair unexpectedly, visit your doctor. Thick hair as a symptom of a pathology or dysfunction is called hirsutism. It's often a sign that you have an underlying condition related to your ovaries or to cortisol or other hormone production.
