Problem 67 - College Physics

Question

The average number of hairs on the normal human scalp is 125000 . A healthy person loses about 65 hairs per day. (New hair from the hair follicle pushes the old hair out.) (a) How many hairs are lost in one month? (b) Pattern baldness (top-of-the-head hair loss) affects about 35 million men in the United States. If an average of \(15 \%\) of the scalp is bald, how many hairs are lost per year by one of these "bald is beautiful" people?

Step-by-Step Solution

Answer

(a) 1982.5 hairs/month; (b) 3,558.75 hairs/year per individual.

Step 1: Calculate Hairs Lost Per Month

To find the number of hairs lost in one month, multiply the number of days in a month by the average number of hairs lost per day. There are 30 or 31 days in a month, but we'll use 30.5 days as an average.So, the calculation is:\[65 \text{ hairs/day} \times 30.5 \text{ days/month} = 1982.5 \text{ hairs/month}\]

Step 2: Calculate Percentage of Scalp that is Bald

For someone with pattern baldness, determine the number of hairs on the part of the scalp that is bald. With 15\% of the scalp being bald:\[0.15 \times 125,000 \text{ hairs} = 18,750 \text{ hairs}.\]

Step 3: Calculate Hairs Lost Per Year for Bald Individuals

Determine how many hairs these bald individuals lose per year from the bald area. Since new hairs grow, assume the bald area continually loses hairs, resulting in the same 18,750 hairs being replaced repeatedly:\[65 \text{ hairs/day}\times 365 \text{ days/year} = 23,725 \text{ hairs/year}.\]Apply the bald percentage:\[0.15 \times 23,725 = 3,558.75 \text{ hairs/year}.\]

Key Concepts

Pattern Baldness

Pattern baldness is a common condition that affects the top of the head. It is characterized by a noticeable thinning or complete lack of hair in this region. This condition is quite prevalent, with around 35 million men in the United States experiencing pattern baldness.
Understanding pattern baldness can help in calculating hair loss. In the exercise provided, an individual with pattern baldness typically has about 15% less hair on their scalp compared to a non-balding individual. This translates to a loss of 18,750 hairs if you assume the average scalp has around 125,000 hairs.
The calculations of hair loss for someone experiencing pattern baldness involve accounting for the hairs lost daily and applying the percentage of the scalp affected by baldness. This offers a clearer picture of how much hair is lost over certain periods, like monthly or annually. Discovering these numbers helps in grasping the degree and impact of pattern baldness.

Hair Follicle Growth

Hair follicle growth is an interesting process where new hair strands are formed inside the follicle, pushed out, and replace older hair. Each hair follicle on the scalp has a lifecycle where the hair grows, rests, and then falls out when a new hair begins to take its place.
Daily hair loss is a natural part of this cycle, with an average person losing about 65 hairs every day. This is because as new hair grows, it ejects the old or shedding hair.

• The follicles are not synchronized, which means while some are shedding, others are growing.
• This automatic and ongoing process ensures that hair continues to grow and replace the old.
• Healthy hair growth is a sign of active follicle cycles.

Understanding how follicles work is crucial to understanding calculations related to hair loss. This scientific insight ties into broader concepts like pattern baldness and the calculation of annual hair loss.

Annual Hair Loss

Annual hair loss calculations become quite informative when assessing the effects of consistent hair shedding over a year. For a non-balding individual, you multiply the daily hair loss by the number of days in a year to obtain total annual hair loss.
When you incorporate the effects of pattern baldness, you adjust these calculations based on the percentage of baldness. In the exercise, it was found that individuals with 15% baldness lose fewer hairs annually than a person with a full head of hair, when specifically considering the bald region.
This involves using the formula for yearly calculation:\[65 \text{ hairs/day} \times 365 \text{ days/year} = 23,725 \text{ hairs/year}\]From which 15% of these hairs could account for annual bald area losses. By multiplying, we see over a year, a bald person might repeatedly lose 3,558.75 of the follicles from this bald section.
Such precise calculations are essential for understanding how baldness affects overall hair loss and can assist in treatment planning or managing expectations for those with scalp hair loss.