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Hair damage can be caused by a variety of things, including hair color, heat-based styling tools and improper care. Damaged hair has a distinctive look and feel that's fairly simple to spot if you know what you're looking for. According to the book "Advanced Hairdressing," there are several tests you can perform on your locks to determine whether they are damaged.

Follicle Test

The follicle test is one way to determine whether your hair is healthy. The website Redbook.com lists this test as a fairly reliable check for hair issues such as styling damage or hereditary hair loss. To perform a follicle test, pluck one strand of hair from your head, gripping it close to your scalp so that the root comes out still attached to the hair. Examine the root end of the strand. If it is bulb-shaped, that means that your hair is strong and healthy. If there is no bulb or if the section is puny, your hair is damaged.

Sink Test

The sink test measures how porous your locks are. Healthy hair is fairly solid, while damaged hair shafts absorb liquid quickly because they are weak. To perform the sink test, pluck four strands of hair from your head: one from the top, one from the back and one from each side. Drop the strands of hair in a container of water. If the strands float, they are quite healthy. If they sink, they are damaged.

Tug test

The tug test measures the elasticity of your hair. Healthy hair is slightly stretchy, while unhealthy hair is brittle and breaks when put under even minor stress. To perform a tug test, dampen a section of your hair. Grip two to three strands between your thumb and forefinger and gently pull on the ends. If it stretches by about one-third of its original length and bounces back when you let go, it's healthy. However, if your hair breaks off, it has suffered some damage to the cortex and is not structurally sound.

Porosity Test

The porosity test determines the condition of your hair cuticle. An undamaged cuticle will feel smooth, but a damaged cuticle with leave hair uneven and coarse. To test your hair's porosity, clamp a section of your hair between your index finger and middle finger. Slide the section of hair through your fingers, going from the tip to the root. If your hair feels rough and uneven, it is damaged. If it feels mostly smooth, the cuticle scales are healthy.