There are different programmed (genetically) growth cycles that hair throughout your body goes through.
For instance, the hair on your head can grow for a good 3-5 years before actually stopping and going through what is known as a follicular dormant stage. Either which way, the hair on your head will not grow much longer than 4-5 feet if let to grow to that extreme.
The hair on your body, limbs, chest, back etc.. has a much shorter growth cycle and is also not as sensitive to DHT (The by-product of testosterone) that limits and inadvertently causes hair loss from the scalp of those prone to hair loss. Yet, unlike the hair on your head, the hair throughout your body, eyebrows included, has a very short growth cycle and thus will only grow to a limited extent before being shed.
*Know that there are physical anomalies, many a times I've seen individuals who will sports a fucking nipple hair (1-strand) that will grow to lengths as long as 6 inches, while the surrounding nipple hair remains at a length of .5-1 inches.*
Be careful with what you do to your eyebrows though, traction alopecia (usually caused by plucking and clipping of hair with mechanical devices) can lead you to lose your eyebrow hair and that would suck..
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