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types of lactose intolerance

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Lactose intolerance may be divided into various groups:

  • congenital lactose intolerance
  • familial lactose intolerance
  • late onset lactose intolerance

Another classification for lactose intolerance is:

  • lactase deficiency has been also been described as primary, secondary, or congenital (1,2,3,4)
    • congenital lactase deficiency is a rare hereditary disorder in which lactase activity is absent

    • primary lactase deficiency is the normal gradual reduction in lactase production seen as an individual matures from infancy into adulthood and is expressed variably across populations
      • usually occurs after 3 years of age in some populations (for example, Africans and Asians) (4)

    • secondary lactase deficiency
      • lactase deficiency may also be a secondary occurrence because of gastroenteritis, bowel surgery, cystic fibrosis, or immune disorders. Lactose intolerance may also occur secondary to epithelium damage caused by other gastroenterological diseases such as in coeliac disease and cow’s milk allergy. It has also been seen transiently in infants exposed to phototherapy and antibiotic therapy
      • (2,3)
        • if a bout of gastroenteritis or use of antibiotics occurs around the time of the GI symptoms, a secondary lactose deficiency should be suspected. In the intestinal insult that often occurs with secondary lactose intolerance, lactase is the first enzyme to be negatively impacted and the last to recover as the insult resolves
        • usually reversible once the epithelial lining has repaired
        • children with suspected lactose intolerance do not usually require any testing and should improve within 48 hours on a low lactose diet (4)
        • in secondary lactose intolerance, for example after severe gastroenteritis, lactose can usually be tolerated again by 6 weeks (4)


  • symptoms occur only in the bowel - for example, abdominal pain, bloating, flatus, and diarrhoea; lactose intolerance does not cause of rectal bleeding (which may occur in cow's milk allergy) (3,4)


  • 1. Host A., Clinical course of cow's milk protein allergy and intolerance. Pediatr Allergy Immunol 1998; 9 (Suppl 11):48-52
  • 2. Host A. Cow's milk protein allergy and intolerance in infancy. Pediatr Allergy Immunol 1994;5:5-36.
  • 3. Wilson J. Milk Intolerance: Lactose Intolerance and Cow's Milk Protein Allergy. Newborn and Infant Nursing Reviews 2005; 5 (4): 203-207.
  • 4. Walsh J et al. Differentiating milk allergy (IgE and non-IgE mediated) from lactose intolerance: understanding the underlying mechanisms and presentations. Br J Gen Pract 2016; DOI: 10.3399/bjgp16X686521

Last edited 03/2020 and last reviewed 03/2020