Causes & Risk Factors

What Causes Microtia? What the Science Currently Shows

Name: What Causes Microtia? Genetic and Environmental Risk Factors
Creator: Arturo Bonilla, MD

Parents deserve clear information without blame. This page explains what research shows about genetics, fetal development, environmental factors, and family risk, while distinguishing a possible risk factor from the cause of an individual child’s microtia.

Information without blame Reported rates vary by population In most children, no single cause can be identified Inner ear is normal in the vast majority of cases

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Dr. Arturo Bonilla with a young microtia patient during consultation at his San Antonio surgical practice

Dr. Arturo Bonilla, MD — Written & Medically Reviewed
Fellowship-Trained · Pediatric Microtia Surgeon · Pediatric Otolaryngologist · Exclusively microtia since 1996 · Last reviewed 2026 · Updated regularly

✓ Medically Reviewed

The most important thing on this page

What Research Shows About Parental Cause

Cases with no identified cause

Most

In most children, no single cause of microtia can be identified.

Discussing possible risk factors

Context

A risk factor does not establish what caused an individual child’s microtia. Questions about health, medications, or exposures deserve an individualized discussion.

Genetic explanations

Vary

Some children have an identifiable genetic cause; others do not. Genetic findings need to be interpreted alongside the child’s clinical features.

Recurrence risk in subsequent pregnancies

Individualized

Family history, associated findings, and any identified genetic cause help guide counseling about future pregnancies.

Parents often wonder whether something during pregnancy caused their child’s microtia. A diagnosis alone cannot answer that question or assign blame. Dr. Bonilla can discuss relevant history and help families focus on their child’s needs and the next steps in care.

“In thirty years of treating children with microtia, I have never seen a case where parental behavior caused the condition. Not once. The question is completely understandable. The answer is always the same.”

— Dr. Arturo Bonilla

The Science of Microtia Development

Fetal Development and Microtia

When the ear forms

The outer ear (auricle or pinna) develops during the first trimester of pregnancy, between approximately weeks 4 and 12 of gestation — with the critical period concentrated in weeks 4 through 8. At this stage, six small tissue swellings called hillocks of His grow from two pharyngeal arches on each side of the developing embryo. These hillocks migrate, fuse, and fold into the distinctive architecture of the human ear.

microtia develops when the outer ear does not form in the usual way before birth. Researchers study genetic changes, developmental pathways, and environmental exposures, but the explanation can differ among children.

Why “we don’t fully know” is an honest answer

Microtia has been studied extensively for decades, and researchers have identified several contributing factors. But the honest scientific statement is that in most children, no single cause of microtia can be identified.¹ ² This is not a failure of medicine — it reflects the extraordinary complexity of embryological development. Hundreds of genes, protein signals, blood vessel patterns, and cell migration events all interact during the window when the ear forms. A disruption in any one of them — or in the delicate coordination between them — can produce microtia without any single identifiable “cause.”

¹ Luquetti DV et al., Birth Defects Res A 2011: a global review of microtia-anotia prevalence.
² Luquetti DV et al., Am J Med Genet A 2012: a review of epidemiology, genetic evidence, and proposed developmental mechanisms. Later studies have identified genetic causes in some patients. Later genetic findings

An unknown cause does not mean that parents failed to do something. Rather than searching for blame, families can discuss relevant history with Dr. Bonilla and focus on hearing assessment, development, and treatment planning.

A proposed mechanism: vascular disruption

One proposed explanation is that altered blood supply during early development contributes to some ear differences. The stapedial artery has been discussed in this context, but this hypothesis is not a confirmed explanation for microtia generally.

Differences in how often microtia affects one side or both sides do not, by themselves, establish a vascular cause. Genetic and other developmental mechanisms are also being investigated.

A vascular hypothesis cannot be used to conclude that a medication, alcohol exposure, or maternal medical condition has no relevance. Specific concerns need to be considered individually.

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Microtia is classified by ICD-10 code Q17.2 as a congenital malformation of the ear. Its occurrence across different populations does not identify or rule out a particular cause for an individual child.

📊 Epidemiology at a Glance

Reported prevalenceVaries by population and study¹

Side affectedRight side more common²

Unilateral vs bilateralOne ear is affected more often than both²

Sex distributionMore common in males²

Isolated microtiaNo additional associated anomalies identified

Syndromic microtiaPart of a recognized syndrome

Specific causeUnknown in most children

ICD-10 codeQ17.2 (microtia), Q16.0 (anotia)

¹ Luquetti DV et al., Birth Defects Res A 2011 — global prevalence review across 92 programs. ² Luquetti DV et al., Am J Med Genet A 2012 — epidemiology and genetics of microtia: incidence, laterality, sex ratio, bilateral rate.

🔎 What Research Shows

A 2023 systematic review identified associations between isolated microtia and several family-history, maternal-health, and exposure factors. These findings do not identify the cause in an individual child or assign parental blame.⁴

⁴ Huang Y et al., Plast Reconstr Surg 2023: 28 articles were included; 22 contributed to meta-analyses. The review reports risk-factor associations, not a blanket exclusion of parental exposures.

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The outer-ear appearance does not establish hearing function. Hearing tests assess each ear and guide the child's hearing plan.

Genetic Factors

What genetics tells us — and what it doesn’t

Genetic factors can contribute to microtia, but their role varies among children.² ⁵ But “genetic” does not necessarily mean “inherited from parents” — and it certainly does not mean “caused by a parent.”

What “genetic” actually means for microtia

Genetic contributions can include a change in a single gene, a chromosome difference, or a combination of genetic influences. Microtia may occur alone or as part of a broader condition. These categories can overlap and do not share one inheritance pattern.

A de novo variant is a new genetic change identified in a child that is not detected in the parents’ tested samples. It may arise in an egg or sperm cell or after fertilization. A genetic counselor can explain the finding and its implications without assigning blame.

Genes associated with microtia

Studies have identified disease-causing variants in some patients with microtia, including variants in HOXA2 and FOXI3. Other genetic diagnoses involve microtia as part of a syndrome. The meaning of a finding depends on the specific variant and the child’s clinical features. Genetic research

There is no single gene that explains every case of microtia. An identified variant can sometimes clarify the diagnosis, but not every variant is disease-causing, and testing does not always provide an answer.

Twin studies: nature’s experiment

Dr. Arturo Bonilla poses with twin brothers from India, both born with bilateral microtia, celebrating the completion of their ear reconstruction surgery at his San Antonio office — one of over 50 countries represented in his practice. — Dr. Bonilla with identical twins from India

A 2009 study of 35 twin pairs recruited through reconstructive centers found that identical twins were more likely than nonidentical twins to both have microtia. However, many identical pairs were not both affected. This supports a genetic contribution without showing that genes alone determine every outcome or proving a specific vascular cause.³

³ Artunduaga MA et al., N Engl J Med 2009: microtia concordance was 38.5% in identical twins versus 4.5% in nonidentical twins in this selected sample. These figures are not recurrence estimates for other families.

Understanding Genetic Factors

Genetic does not always mean inherited
A genetic change may be inherited or arise for the first time in a child. A genetic finding does not imply parental fault.

Microtia without other associated findings
Genetic factors may contribute even when microtia occurs without an identified syndrome. Testing does not always reveal a specific cause.

Microtia with additional findings
When microtia occurs with other developmental differences, a genetic evaluation may help determine whether an underlying syndrome is present.

An individualized discussion
Dr. Bonilla can review your child’s findings and family history and discuss whether a referral for genetic counseling would be helpful.

Most common scenario

No identified cause

A child can have microtia without a specific cause being identified. The absence of a diagnosis does not exclude a genetic contribution.

Most

children have no single identified cause

Syndromic cases

Part of a broader syndrome

Microtia can occur as part of a recognized syndrome or alongside other developmental findings. Additional findings do not automatically establish a syndrome.

Varies

assessment depends on the child’s findings

Environmental Factors

Environmental Factors — What the Research Shows

Researchers have studied maternal health, medications, nutrition, and environmental exposures in relation to microtia. Evidence varies by factor, and a population-level association cannot determine what caused an individual child’s condition.

What the evidence actually shows

Studies have examined medications, maternal medical conditions, nutrition, and environmental exposures. Some findings are associations; certain medications are established causes of birth defects. These are different levels of evidence and should not be treated as interchangeable.

Questions about an exposure deserve a specific review, not a blanket answer. Dr. Bonilla can discuss concerns related to microtia; an obstetric clinician or prescribing clinician can advise on pregnancy and medication safety.

Isotretinoin (Accutane) and fetal risk

Isotretinoin, historically known by the brand name Accutane, is a recognized cause of severe birth defects, including ear abnormalities, when used during pregnancy. It must not be used during pregnancy, and the United States uses the iPLEDGE program to reduce fetal exposure. A possible exposure during treatment or within one month after stopping requires prompt advice from the prescribing clinician and obstetric clinician.

FDA prescribing information and iPLEDGE guidance describe isotretinoin’s fetal risks and pregnancy-prevention requirements.

Maternal diabetes

Diabetes present before pregnancy has been associated with microtia and other birth defects. Findings depend on the type of diabetes and the population studied. A diabetes diagnosis or a history of good glucose control cannot establish or exclude the cause in an individual child. Pregnancy planning and glucose management should be discussed with the clinician managing the diabetes.

Altitude and geographic variation

Higher rates of microtia have been documented in populations living at high altitude — including parts of Peru, Bolivia, and other Andean communities. Researchers hypothesize that reduced oxygen availability at high altitude may affect vascular development in the embryo. This finding is epidemiological and population-level; it does not identify anything any individual parent could have done differently.

What the evidence does NOT show

A study that does not find an association with microtia does not prove that an exposure is safe during pregnancy. Evidence varies by the substance, dose, timing, and outcome studied. There is no established safe amount of alcohol during pregnancy, and medications should be reviewed individually with the prescribing clinician. Concerns about a past exposure deserve support and an individualized assessment, not blame.

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The outer ear begins developing early in pregnancy, sometimes before pregnancy is recognized. Early timing does not identify a cause or make current care unimportant. Discuss concerns with the appropriate clinician and continue recommended prenatal care.

Environmental risk factors — evidence review

Factor	Evidence / limits	Practical interpretation
Isotretinoin	Established fetal risk, including ear abnormalities	Must not be used in pregnancy; possible exposure needs prompt clinical advice
Diabetes before pregnancy	Associated with microtia in population studies	Glucose-control history does not establish an individual cause
High altitude	Population-level association	Does not identify the cause in an individual child
Thalidomide	Established fetal risk; still used under restrictions	Contraindicated in pregnancy
Pesticide exposure	Limited evidence of association in a 2023 review	Review the specific product and exposure history
Alcohol	Microtia findings do not establish pregnancy safety	Avoid alcohol during pregnancy
Caffeine	No blanket safety conclusion from this microtia review	Discuss pregnancy guidance with the obstetric clinician
Stress / anxiety	A personal history alone does not establish cause	Seek support without assigning blame
Exercise / physical activity	A personal history alone does not establish cause	Follow individualized pregnancy advice
Common OTC medications	Risk depends on the specific medicine and exposure	Review the product, dose, and timing with a clinician
Prenatal vitamins / nutrition	Some nutritional associations have been reported	A missed vitamin does not establish a cause; follow prenatal advice

This table distinguishes known fetal hazards from population associations and uncertainty. It is not a tool for diagnosing the cause of a child’s microtia or deciding whether a medicine is safe during pregnancy. Do not change prescribed treatment based on this table; contact the prescribing clinician for advice.
Huang review; Thalidomide prescribing information; Pregnancy alcohol guidance; Maternal nutrition study

Bilateral vs. Unilateral

Why microtia is almost always one-sided — and what it means when it isn’t

Microtia more often affects one ear than both. This pattern describes how the condition presents; it does not identify its cause in an individual child.

One ear

Unilateral presentation

Unilateral microtia — one ear affected

Right ear affected more often than left
The opposite ear also needs hearing assessment and monitoring
Monitor speech, language, and classroom listening even when the opposite ear hears normally
A one-sided ear difference does not rule out a genetic contribution
Hearing tests assess function on the affected side

Both ears

Bilateral presentation

Bilateral microtia — both ears affected

Bilateral microtia can occur with additional findings; genetic evaluation may help clarify the diagnosis
Prompt hearing assessment is essential. For infants with bilateral aural atresia, Dr. Bonilla recommends softband fitting within the first two months, coordinated with diagnostic testing and pediatric audiology
Early hearing care supports development; follow-up identifies any additional communication needs
Anotia can affect one ear or both
Bilateral microtia may warrant genetic evaluation; recurrence risk depends on the individual findings and family history.

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One-sided microtia does not prove or rule out a particular cause. Genetic conditions can affect one ear or both, and the pattern alone cannot determine whether an exposure contributed. Dr. Bonilla can consider the ear findings together with the child’s medical and family history.

Family Recurrence Risk

Does microtia run in families? What are the chances for a future pregnancy?

The short answer: it can, but usually doesn’t

Microtia does not have one inheritance pattern that applies to every child. Some cases occur as part of an inherited condition, while others arise without a known family history. The appearance of the ear alone cannot establish the chance of microtia occurring in a future pregnancy.

The chance of microtia occurring in another child depends on the family history, the child’s associated findings, and whether a specific genetic cause has been identified. One percentage cannot accurately describe every family’s situation. Dr. Bonilla can discuss these factors and whether a referral for genetic counseling would help you understand the implications for a future pregnancy.

When genetics consultation is most valuable

Genetic counseling may be especially helpful when a child has bilateral microtia, other findings suggesting a syndrome, or a family history of microtia or related differences. Families considering another pregnancy may also find counseling helpful. Dr. Bonilla can discuss whether a referral is appropriate, including for children with isolated unilateral microtia. An evaluation may clarify risk, although a precise estimate is not always possible.

Microtia in other family members

Microtia can occur in more than one family member, sometimes with differences in how the ears are affected. A family history may suggest an inherited contribution, but it does not by itself establish a particular inheritance pattern or predict the chance of another affected child. Tell Dr. Bonilla about relatives with microtia or other ear differences so this information can inform an individualized assessment.

What genetics cannot tell you

Genetic testing may identify a cause, return an uncertain finding, or find no explanation. Whole exome sequencing examines protein-coding regions of many genes; it is not limited to checking previously known mutations. A negative result does not exclude every genetic cause. A genetic specialist can explain the limitations of the test and whether further evaluation or later reanalysis may be useful.

📊 Recurrence Risk Summary

Background riskPopulation frequency is not an individual recurrence estimate

Isolated unilateralIndividual assessment; ear appearance alone does not determine risk

Isolated bilateralGenetic evaluation may help clarify risk

Syndromic (known gene)Depends on the specific diagnosis and inheritance pattern

With family historyFamily history informs individualized genetic counseling

Prenatal diagnosisMay be seen on ultrasound; can be missed

Genetics consult?Discuss a referral with Dr. Bonilla

A word on recurrence anxiety

“Parents who have had one child with microtia are often terrified during subsequent pregnancies. It is worth remembering that even with a slightly elevated risk, the great majority of subsequent pregnancies are unaffected. Worry is natural — but the odds are genuinely reassuring.”

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A clinical geneticist or genetic counselor can help interpret your family history, your child’s findings, and any genetic test results. Dr. Bonilla can discuss a referral if you have questions about future pregnancies. Sometimes the evaluation clarifies risk; sometimes uncertainty remains.

Associated Conditions

Conditions sometimes seen alongside microtia

Microtia can occur on its own, with other developmental findings, or as part of a recognized syndrome. Having another finding does not automatically mean a child has a syndrome. The conditions below are examples that may be considered during evaluation; their presence and significance must be assessed individually.

The examination checks for associated findings beyond the ears. Depending on the child's findings and local clinical practice, a clinician may recommend a renal ultrasound to assess the kidneys. Any abnormal result needs interpretation and appropriate follow-up.

Facial asymmetry and jaw abnormalities are more common in children with microtia than in the general population, reflecting the shared embryological origin of the ear and jaw. In most cases these are minor and cosmetically unimportant; in more significant cases (as with hemifacial microsomia) separate evaluation and management may be indicated.

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“Isolated microtia” means no additional associated anomalies have been identified. The list below describes possible associated findings, not diagnoses that apply to every child. Dr. Bonilla can discuss which evaluations are appropriate.

Associated conditions can affect evaluation, anesthesia, surgical timing, or reconstruction planning. Dr. Bonilla reviews each child's needs and coordinates with other specialists when appropriate.

Atresia (absent ear canal)

Common alongside microtia

Aural atresia is an absent ear canal and commonly occurs with microtia. Canal narrowing is called stenosis. Hearing tests and specialist assessment guide management.

Hemifacial Microsomia

Uncommon

Underdevelopment of one side of the face, including the jaw, cheek, and facial muscles. Shares embryological origin with microtia. Ranges from subtle to significant. Evaluated by craniofacial team. Reconstruction eligibility and planning are assessed individually.

Treacher Collins Syndrome

Rare

A genetic syndrome (usually TCOF1 mutation) involving bilateral facial underdevelopment including both ears, cheekbones, and jaw. Bilateral microtia is typical. Identified early; requires multidisciplinary care.

Goldenhar Syndrome (OAV)

Rare

Oculo-auriculo-vertebral spectrum includes microtia alongside eye abnormalities and vertebral differences. Cause poorly understood; mostly sporadic. Associated findings are considered in reconstruction planning.

CHARGE Syndrome

Rare

CHD7 gene mutation causing Coloboma, Heart defects, choanal Atresia, growth Restriction, Genital abnormalities, and Ear anomalies (including microtia). Identified by pediatric geneticist. Complex multisystem management.

Renal (Kidney) Anomalies

Sometimes screened

Kidney differences can occur with microtia, including outside a recognized syndrome. A clinician can discuss renal ultrasound screening and any follow-up indicated by the findings. Renal screening study

Facial Palsy (Facial Nerve)

Rare

Partial facial nerve involvement can occur in some syndromic microtia cases. Evaluated by the surgical team before any ear surgery since the facial nerve passes near the surgical field. Its significance for reconstruction is assessed individually.

Macrotia / Preauricular Tags

Occasional finding

Small skin tags or pits in front of the ear (preauricular tags or pits) may be present. Usually isolated and minor. Sometimes associated with hearing screening abnormalities. Often removed as a simple outpatient procedure.

Cleft Lip / Palate

Rare

Some craniofacial syndromes include both microtia and clefting. When both are present, the cleft is typically repaired first in infancy, followed by ear reconstruction at appropriate age. Treatment sequencing is coordinated with the specialists involved.

What to Do Next

Related Resources

Now that you understand the causes and risk factors, these are the most useful next resources depending on where you are in your journey.

For Parents

A Parent’s Complete Guide to Microtia

Emotional support, practical steps, age-by-age guidance, school and social considerations, and the path to reconstruction.

Read the guide →

The Diagnosis

The Four Grades of Microtia Explained

What Grade I through Grade IV mean, how each affects hearing, and what Dr. Bonilla’s reconstruction produces for each grade.

Understand the grades →

Hearing

Microtia and Hearing Loss — What Parents Need to Know

Why the hearing loss in microtia is almost always conductive, what BAHA provides, and how to support your child’s hearing development.

Learn about hearing →

The Reconstruction

How Dr. Bonilla Rebuilds the Ear — Stage by Stage

The complete two-stage rib cartilage surgical process, from framework harvest through elevation. What actually happens in the operating room.

Explore the technique →

Just Diagnosed

Just Found Out Your Child Has Microtia

For parents in the first hours and days after diagnosis. What to do first, what to worry about, and what can wait.

Read now →

Talk to Dr. Bonilla

Contact Dr. Bonilla

A consultation gives your family a specific plan — grade assessment, surgical timing, hearing options, honest expectations. Telehealth available worldwide.

Schedule a consultation →

Next Steps

Understanding possible causes should support your family, not assign blame. Dr. Bonilla can help you plan the next steps for hearing assessment and, when appropriate, ear reconstruction. Telehealth is available worldwide. Visit Microtia.net to learn more about Dr. Bonilla’s dedicated microtia practice.

Contact Dr. Bonilla Call (210) 477‑3277

Peer-Reviewed Literature

References

1
Luquetti DV, Leoncini E, Mastroiacovo P. Microtia-Anotia: A Global Review of Prevalence Rates. Birth Defects Res A Clin Mol Teratol. 2011;91(9):813–822.
PMID: 21656661 ↗
2
Luquetti DV, Heike CL, Hing AV, Cunningham ML, Cox TC. Microtia: Epidemiology and Genetics. Am J Med Genet A. 2012;158A(1):124–139.
PMID: 22106030 ↗
3
Artunduaga MA, Quintanilla-Dieck MD, Greenway S, et al. A Classic Twin Study of External Ear Malformations, Including Microtia. N Engl J Med. 2009;361(12):1216–1218.
PMID: 19759387 ↗
4
Huang Y, Huang X, Li K, Yang Q. Risk Factors of Isolated Microtia: A Systematic Review and Meta-Analysis. Plast Reconstr Surg. 2023;151(4):651e–663e.
PMID: 36729823 ↗
5
Wahdini SI, Idamatussilmi F, Pramanasari R, et al. Genotype-Phenotype Associations in Microtia: A Systematic Review. Orphanet J Rare Dis. 2024;19:152.
PMID: 38594752 ↗