This article features questions regarding logarithmic functions and hair growth. The first question is, "What is the underlying natural phenomenon that causes the natural log function to show up so frequently in scientific equations?" There are two reasons for this. The first is simply that the logarithm of a number is often used as a replacement for the number itself in order to keep the size of the number manageable. Nature has a lot of large and small numbers to contend with. Other examples of logarithmic applications include the star brightness (magnitude) and sound volume (decibels). Not all scales are logarithmic; for instance, the MOHS mineral hardness scale based on the relative ability of one mineral to scratch another. The natural logarithm is the inverse of the exponential function. This leads to the second reason, namely, that that exponential growth and decay occur often in nature. Exponential growth or decay occur whenever the time rate of change of a quantity is directly proportional to the quantity itself. Exponential behavior is common, and hence its inverse function--the natural logarithm--often appears in scientific equations. The second question is, "Why do some hairs on the human body grow indefinitely while others grow to a certain length and then stop?" Along with it, "How does hair know when to stop?" Variation in the growth rate of hair is well documented and appears to be under genetic control. Hair growth occurs in a three-phase cycle: anagen, catagen, and telogen. Here, the focus is on anagen, the growth phase, and telogen, the resting phase in which no significant growth occurs. The length of anagen phase for body and eye hair is the same among individuals. However, the length of anagen phase for scalp hair is variable. The only signal that has been implicated in controlling the length of anagen phase is fibroblast growth factor 5 (FGF5). FGF5 is a secreted signaling protein that localizes to a specific region, the outer root sheath, of hair follicles during anagen phase. Research suggests that FGF5 inhibits hair growth and the length of the growth phase for hair is under genetic control. There are a couple other factors that determine ultimate hair length. Among them are hair wearing and breaking through the ordinary stresses of life; and our inclination to shave and cut our hair. This aside, hair itself clearly has an inherent tendency toward long or short.