Split end as viewed under a microscope.

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Chemically bleached hair. The cuticle (outside) should look like little shingles. You can see this cuticle is rough and disorganized.

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The same bleached hair strand, dyed with henndigo (henna + indigo). The cuticle is still disorganized, but you can see it's smoothed by the henna coating.

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Chemically dyed hair. Note the rough edges. Chemical dye actually lifts the "shingles" of the cuticles, deposits dye inside then closes them back again. They don't close tightly.

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Chemically dyed hair near the root, where the damage isn't as obvious yet.

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Chemically dyed hair with henna applied. The cuticle is smoother now.

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Same hair as just above, with the microscope focused to show the coating of henna (what looks like a blue line outside of the strand).

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Hennaed hair with better view of how the cuticle should look. Note that the cuticle overlaps and looks like shingles to prevent water entering and damaging the inside of the hair shaft.