Hypotrichosis is the term dermatologists use to describe a condition of no
hair growth. Unlike alopecia, which describes hair loss where formerly there
was hair growth, hypotrichosis describes a situation where there wasn't any
hair growth in the first place. Hypotrichoses (plural) then are conditions that
affect individuals right from birth and usually stay with them throughout their
The majority of hypotrichoses are due to genetic aberrations or defects of
embryonic development. There are hundreds of types of genetic hypotrichoses.
Often, affected individuals have other physical or mental problems beyond a
lack of hair. Conditions such as Graham-Little syndrome, Ofuji syndrome,
cartilage-hair hypoplasia, Jeanselme and Rime hypotrichosis, Marie Unna
hypotrichosis, and metaphyseal chondrodysplasia, among many others, can involve
the symptom of hypotrichosis.
With the rapidly improving understanding of the human genome, our
comprehension of why and how genetic defects cause hair loss and other symptoms
is growing. But, while we may understand the genetics and the biochemistry
behind hypotrichoses, treating them is very difficult. Most conditions
involving hypotrichosis have no known treatment.
A few forms of hypotrichosis are worth mentioning, either because they are
relatively common or because they are interesting in terms of understanding
Aplasia cutis congenita, or congenital aplasia, is a developmental defect
where, for reasons not understood, the skin does not fully form as an embryo
develops. A baby may be born with a patch of skin that is like an open wound or
an ulcer. Often this defect occurs at the back of the scalp, at the center of
the "whorl pattern" of hair growth. If the defect is small, the skin will scab
over and the baby is left with a scar.
Sometimes this happens in the womb and all that can be seen at birth is a
patch of scalp where there are no hair follicles. However, if a baby is born
with a large congenital aplasia, it usually requires an operation to cut out
the affected area and close up the skin. This is often done with some urgency,
since the open wound is a site of potential hemorrhage and infection. The
quicker the defect heals, the better.
Triangular alopecia (alopecia triangularis) is a condition similar to
congenital aplasia. It is usually apparent from birth and tends to affect a
triangular patch of skin and hair above the temples. For unknown reasons, the
skin fails to grow hair follicles in this area in a few people. While babies
are not born with open ulcers as with aplasia cutis congenita, the long-term
result is much the same -- a bald patch where hair does not grow. The affected
area can be surgically removed or implanted with hair follicles taken from
elsewhere on the scalp.