Baby oil is essentially a scented compound derived from mineral oil and used to help with various irritations that toddlers receive from cribs and other such surfaces. The product is also used as a quick moisturizer for skin and hair for adults. In hair, baby oil acts as other grease and oil-based products, making the hair shine but also adding greasiness.
As a moisturizer, baby oil is very good for helping with dry and brittle hair. However, the oil should be used sparingly, as too much of it makes the hair greasy and heavy. Generally, baby oil is not the best product to use, as others are available for use specifically on dry hair that don't have the same greasy aftereffects.
Baby oil provides a neat shine when applied to hair; however, as with using the product on dry hair, too much leads to over-greasing and a heavy, washed look all day. For the best effect, a small amount of baby oil should be applied just after washing, while the hair is still wet, and before blow drying. This provides the shining effect with minimal residual grease.
One of the problems with using baby oil on hair is that the substance remains there until it's washed away. Once the oil is applied, especially if it's a little too much for the hair to process, it sits there the entire day and accumulates with the hair natural oils over the day. Washing removes the baby oil.
As with using baby oil on infants, the oil has a tendency to stain surfaces it touches. Using excessive baby oil on hair could lead to staining of clothes that come in contact with the hair, headrests, cars and so forth. Unlike washing the oil out of hair, these stains aren't always easily removed. Similarly, the oil may wipe from hair to skin, making the skin, especially that of the face, greasy and possibly clogging pores, which can lead to blemishes.