Behavior & Social

Autism Signs Appearing After 18 Months

Medically reviewed by Dr. Emily Torres, PhD, CCC-SLP · Pediatric Speech-Language Pathologist

Content reviewed against published AAP, CDC, NIH guidelines

Editorial policy

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Behavioral development varies greatly from child to child. If you have noticed autism signs appearing after 18 months, here is what you need to know.

The short answer

While some children show signs of autism from early infancy, others develop typically until 12 to 24 months before differences emerge. This can involve regression (losing skills) or plateau (skills stop progressing while peers advance). Late-appearing signs are valid and important to recognize. If you notice changes in your child's development after 18 months, request evaluation.

Key takeaways

  • While some children show signs of autism from early infancy, others develop typically until 12 to 24 months before differences emerge. This can involve regression (losing skills) or plateau (skills stop progressing while peers advance). Late-appearing signs are valid and important to recognize. If you notice changes in your child's development after 18 months, request evaluation.
  • Usually normal when: Your child is developing new skills steadily even if at a slightly slower pace
  • Call your doctor if: Your child has clearly lost previously acquired skills like words, social smiling, or gestures
  • Varies by age — see the age-by-age breakdown below

This is one of the most common questions parents ask. Searching for answers means you care.

What Parents Should Know

According to AAP, CDC, NIH guidelines, while some children show signs of autism from early infancy, others develop typically until 12 to 24 months before differences emerge. This can involve regression (losing skills) or plateau (skills stop progressing while peers advance). Late-appearing signs are valid and important to recognize. If you notice changes in your child's development after 18 months, request evaluation. At 0-12 months, development may appear completely typical. The child makes eye contact, babbles, and engages socially. Some subtle differences may only be recognized in retrospect after a later diagnosis. It is generally considered normal when your child is developing new skills steadily even if at a slightly slower pace. However, you should contact your pediatrician promptly if your child has clearly lost previously acquired skills like words, social smiling, or gestures.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your child is developing new skills steadily even if at a slightly slower pace
Your child has clearly lost previously acquired skills like words, social smiling, or gestures
Your child temporarily regresses during illness or stress but bounces back
Your child's development has regressed significantly in multiple areas
Your child has a brief plateau in one area but is progressing in others
Your child has stopped adding new words or skills for several months

By Age

What to expect by age

0-12 months

Development may appear completely typical. The child makes eye contact, babbles, and engages socially. Some subtle differences may only be recognized in retrospect after a later diagnosis.

12-18 months

Some children begin to show differences in this period. Language development may slow, social engagement may decrease, or the child may not add expected milestones like pointing and showing.

18-24 months

This is the most common window for autism signs to become apparent to parents. Changes may include fewer words or lost words, decreased eye contact, less interest in others, new repetitive behaviors, or failure to develop pretend play.

24-36 months

Differences become more obvious as social demands increase. The gap between the child and typically developing peers widens. Evaluation is recommended even if the child had a period of typical development.

3-5 years

Some higher-functioning children are not identified until school demands increase. Late identification does not mean milder autism; it may mean the signs were more subtle or were attributed to other factors.

What to Tell Your Pediatrician

  • Describe when you first noticed autism signs appearing after 18 months and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your child has stopped adding new words or skills for several months.
  • Mention if your child seems less socially engaged than they were a few months ago.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your child is developing new skills steadily even if at a slightly slower pace
  • Your child temporarily regresses during illness or stress but bounces back
  • Your child has a brief plateau in one area but is progressing in others
Mention at your next visit when...
  • Your child has stopped adding new words or skills for several months
  • Your child seems less socially engaged than they were a few months ago
  • You notice new repetitive behaviors appearing alongside slowed development
Act now when...
  • Your child has clearly lost previously acquired skills like words, social smiling, or gestures
  • Your child's development has regressed significantly in multiple areas

What You Can Do at Home

  • Keep track of when you notice autism signs appearing after 18 months — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your child is developing new skills steadily even if at a slightly slower pace — this is generally within the range of normal.
  • At 0-12 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Respond consistently and calmly to your baby's behavior. Maintain predictable daily routines.
  • While monitoring at home, seek immediate care if your child has clearly lost previously acquired skills like words, social smiling, or gestures.

Autistic Regression - Losing Skills

Approximately 25 to 30% of children later diagnosed with autism experience a regression, losing previously acquired skills between 15 and 24 months. This most commonly affects language and social skills. Any loss of skills at any age requires prompt medical evaluation. While regression can occur in autism, it can also indicate other medical conditions that need to be ruled out.

Worried About Autism - When and How to Screen

The AAP recommends autism screening at 18 and 24 months for all children, using the M-CHAT-R/F questionnaire. If you have concerns before these ages, you can request screening earlier. Early signs of autism may include limited eye contact, no pointing by 12 months, no words by 16 months, no pretend play by 18 months, or loss of any previously acquired skills. Trust your instincts as a parent and raise concerns with your pediatrician.

My Baby Is Losing Words or Skills

If your child was consistently using words and has truly stopped, this is something to act on promptly. Regression - the genuine loss of skills a child previously had - is different from a normal plateau or a toddler being too busy to talk, and it always warrants a conversation with your pediatrician sooner rather than later.

Milestone

Milestone Checklists by Age

Track your baby's developmental milestones from birth to 5 years with age-specific checklists.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is autism signs appearing after 18 months normal?
While some children show signs of autism from early infancy, others develop typically until 12 to 24 months before differences emerge. This can involve regression (losing skills) or plateau (skills stop progressing while peers advance). Late-appearing signs are valid and important to recognize. If you notice changes in your child's development after 18 months, request evaluation.
When should I call the doctor about autism signs appearing after 18 months?
Your child has clearly lost previously acquired skills like words, social smiling, or gestures Your child's development has regressed significantly in multiple areas
When is autism signs appearing after 18 months normal?
Your child is developing new skills steadily even if at a slightly slower pace Your child temporarily regresses during illness or stress but bounces back Your child has a brief plateau in one area but is progressing in others
What causes autism signs appearing after 18 months?
While some children show signs of autism from early infancy, others develop typically until 12 to 24 months before differences emerge. This can involve regression (losing skills) or plateau (skills stop progressing while peers advance). Late-appearing signs are valid and important to recognize. If you notice changes in your child's development after 18 months, request evaluation. Common explanations include: Your child is developing new skills steadily even if at a slightly slower pace. Your child temporarily regresses during illness or stress but bounces back.
What should I mention to my pediatrician about autism signs appearing after 18 months?
You should mention autism signs appearing after 18 months at your next visit if: Your child has stopped adding new words or skills for several months. Your child seems less socially engaged than they were a few months ago. You notice new repetitive behaviors appearing alongside slowed development.
Is autism signs appearing after 18 months normal at 0-12 months?
Development may appear completely typical. The child makes eye contact, babbles, and engages socially. Some subtle differences may only be recognized in retrospect after a later diagnosis.
Is autism signs appearing after 18 months normal at 12-18 months?
Some children begin to show differences in this period. Language development may slow, social engagement may decrease, or the child may not add expected milestones like pointing and showing.
Should I go to the ER for autism signs appearing after 18 months?
Seek emergency care if your child has clearly lost previously acquired skills like words, social smiling, or gestures, or if your child's development has regressed significantly in multiple areas. When in doubt, call your pediatrician's after-hours line for guidance.
Does autism signs appearing after 18 months go away on its own?
In many cases, autism signs appearing after 18 months resolves on its own, especially when your child is developing new skills steadily even if at a slightly slower pace. By 3-5 years, some higher-functioning children are not identified until school demands increase. Late identification does not mean milder autism; it may mean the signs were more subtle or were attributed to other factors.
AAPCDCNIH

References

  1. [1]American Academy of Pediatrics. When Autism Signs Appear Later. AAP
  2. [2]Centers for Disease Control and Prevention. Signs and Symptoms of Autism. CDC
  3. [3]National Institute of Mental Health. Autism Spectrum Disorder. NIH

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Autism Signs Appearing After 18 Months.

Things to mention

  • Describe when you first noticed autism signs appearing after 18 months and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your child has stopped adding new words or skills for several months.
  • Mention if your child seems less socially engaged than they were a few months ago.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your child has stopped adding new words or skills for several months
  • Your child seems less socially engaged than they were a few months ago
  • You notice new repetitive behaviors appearing alongside slowed development

Urgent signs to report immediately

  • Your child has clearly lost previously acquired skills like words, social smiling, or gestures
  • Your child's development has regressed significantly in multiple areas

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Ear Infection TriageMilestone ChecklistsEarly Intervention DirectoryBaby Sign Language GuideBaby Tracker

Bottom line

Most cases of autism signs appearing after 18 months are normal. Talk to your pediatrician if your child has clearly lost previously acquired skills like words, social smiling, or gestures.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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Autistic Regression - Losing Skills

Approximately 25 to 30% of children later diagnosed with autism experience a regression, losing previously acquired skills between 15 and 24 months. This most commonly affects language and social skills. Any loss of skills at any age requires prompt medical evaluation. While regression can occur in autism, it can also indicate other medical conditions that need to be ruled out.

Worried About Autism - When and How to Screen

The AAP recommends autism screening at 18 and 24 months for all children, using the M-CHAT-R/F questionnaire. If you have concerns before these ages, you can request screening earlier. Early signs of autism may include limited eye contact, no pointing by 12 months, no words by 16 months, no pretend play by 18 months, or loss of any previously acquired skills. Trust your instincts as a parent and raise concerns with your pediatrician.

My Baby Is Losing Words or Skills

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