Fetal alcohol syndrome (FAS) produces a recognizable pattern of facial features, smaller body size, and brain-related differences that begin before birth and last a lifetime. The facial signs are subtle, not dramatic, and they can be easy to miss if you don’t know what to look for. Here’s what distinguishes FAS physically, how it affects growth and development, and how the appearance can shift with age.
The Three Signature Facial Features
Diagnosis of FAS centers on three specific facial markers that, taken together, create a distinctive look. No single feature on its own confirms the condition. All three need to be present and fall at the extreme end of normal variation.
Short eye openings. The horizontal distance from the inner corner to the outer corner of each eye is measurably smaller than average. This makes the eyes appear small or narrow. Clinicians measure this in millimeters and compare it to age-matched norms. To meet diagnostic criteria, the measurement typically falls two or more standard deviations below the population average for the child’s age.
Smooth philtrum. The philtrum is the vertical groove that runs from the base of the nose to the top of the upper lip. Most people have a clearly defined groove with visible ridges on either side. In FAS, this groove is partially or completely flattened out, leaving the skin between the nose and lip looking smooth and featureless. Clinicians grade this on a 5-point pictorial scale developed at the University of Washington, where a rank of 1 means a deeply grooved philtrum and a rank of 5 means completely smooth. A rank of 4 or 5 is characteristic of FAS.
Thin upper lip. The red, visible portion of the upper lip (the vermilion border) is noticeably thin. On the same 5-point scale, a rank of 4 or 5 represents the thinnest end of the spectrum. The combination of a thin lip and smooth philtrum gives the mid-face a flat, underdefined appearance. One important detail: these features must be assessed with a relaxed, neutral expression. Smiling changes both lip thickness and philtrum shape enough to throw off the reading.
Some children also have a flat nasal bridge, which adds to the overall flat look of the midface. This isn’t one of the three core diagnostic markers, but it’s commonly noted alongside them.
Smaller Body Size
Children with FAS are often small for their age, both in height and weight. The diagnostic threshold is a height or weight at or below the 10th percentile on standard growth charts, meaning 90% of children the same age are larger. This growth deficit can start in the womb and continue after birth. Some children are born small and stay small; others fall behind gradually during early childhood.
Head size follows a similar pattern. A head circumference below the 10th percentile is a recognized sign of the condition. If a child is already small overall, clinicians look for the head to be disproportionately small compared to the rest of the body, typically at or below the 3rd percentile. A small head often reflects reduced brain volume, which connects directly to the neurological effects of prenatal alcohol exposure.
Brain and Developmental Differences
The physical appearance of FAS extends beyond what you see on the outside. Brain imaging studies show measurable structural changes, including a smaller overall brain, a reduced or abnormally shaped corpus callosum (the band of tissue connecting the two brain hemispheres), and differences in the cerebellum and deep brain structures involved in movement and coordination.
These structural changes show up as functional problems in daily life. Children with FAS often have difficulty with memory, attention, impulse control, and reasoning. Language development and motor coordination can lag behind peers. Learning disabilities are common, and many children struggle with math and abstract thinking in particular. Behavioral challenges like difficulty reading social cues, poor judgment, and trouble adapting to new situations tend to become more apparent in school-age years.
The degree of brain involvement doesn’t always match the severity of facial features. Some children have all three facial markers but relatively mild cognitive effects. Others have significant brain-based difficulties with only subtle facial signs, a pattern that falls under the broader umbrella of fetal alcohol spectrum disorders.
How the Appearance Changes With Age
The characteristic facial features of FAS are most recognizable in young children, roughly between ages 2 and 10. During this window, the short eye openings, smooth philtrum, and thin upper lip are at their most distinctive. As children enter puberty and the face grows and changes, these features can become harder to spot. The philtrum may develop slightly more definition, the face elongates, and the overall proportions shift.
This doesn’t mean the condition resolves. The symptoms of FAS are lifelong. Growth may remain below average into adulthood, and the neurological effects persist. But the window for recognizing FAS from facial appearance alone narrows as a person gets older, which is one reason early diagnosis matters so much.
The Full Spectrum Beyond Classic FAS
Not everyone affected by prenatal alcohol exposure looks like a textbook case. FAS sits at one end of a broader spectrum called fetal alcohol spectrum disorders (FASD). A person can have significant brain damage from alcohol exposure without meeting the full facial criteria for FAS.
Older terminology used the label “partial FAS” for cases where only some facial features were present, but this term has fallen out of favor. It was frequently misunderstood as a milder condition, when in reality the brain damage could be just as severe as in full FAS. Current diagnostic frameworks group outcomes into categories based on the combination of facial features, growth patterns, and level of brain involvement, each scored independently.
For people on the spectrum who lack the classic facial features, the condition is essentially invisible. There is no distinctive “look” to identify them, which makes behavioral and cognitive assessment the primary path to diagnosis. This is a significant challenge, since many of these individuals go undiagnosed and miss out on early support services that could meaningfully change their outcomes.
Other Physical Signs
Beyond the face, growth, and brain, FAS can affect the development of other organ systems. Heart defects, kidney abnormalities, and bone or joint problems are reported in some cases. Vision and hearing difficulties are also more common than in the general population. These features vary widely from person to person and aren’t part of the core diagnostic criteria, but they contribute to the overall clinical picture.
Skeletal differences can include problems with finger or toe formation and, less commonly, spinal abnormalities. Some children have a characteristic pattern of small, curved pinky fingers or limited range of motion in certain joints. These signs are not specific enough to FAS to be diagnostic on their own, but when they appear alongside the facial features and growth deficits, they add supporting evidence.