Methemoglobinemia is a blood disorder in which too little oxygen is delivered to your cells. An individual may be born with it, or it may be caused by exposure to certain medicines, chemicals, or foods.

Oxygen is carried through your bloodstream by hemoglobin, a protein that’s attached to your red blood cells. Normally, hemoglobin then releases that oxygen to cells throughout your body.

However, there’s a specific type of hemoglobin known as methemoglobin that carries oxygen through your blood but doesn’t release it to the cells. If your body produces too much methemoglobin, it can begin to replace your normal hemoglobin. This can lead to not enough oxygen getting to your cells.

There are two types of methemoglobinemia: acquired and congenital. Keep reading to learn more about what causes each type of methemoglobinemia, plus its symptoms and treatment.

Symptoms of methemoglobinemia may vary depending on which type you have. The main symptoms are:

  • cyanosis, which describes a bluish color of the skin, especially the lips and fingers
  • chocolate-brown colored blood

It’s because of cyanosis that some people call methemoglobinemia “baby blue syndrome.”

As methemoglobin levels increase, symptoms continue to get more serious. These can include:

  • headache
  • shortness of breath
  • nausea
  • rapid heart rate
  • fatigue and lethargy
  • confusion or stupor
  • loss of consciousness

Methemoglobinemia can be congenital, which means you’re born with the condition. Congenital methemoglobinemia is caused by a genetic defect that you inherit from your parents. This genetic defect leads to a deficiency of a certain enzyme, or protein. This protein is responsible for converting methemoglobin to hemoglobin. Congenital methemoglobinemia is much less common than the acquired form of the condition.

There are three types of congenital methemoglobinemia.

Type 1

Type 1 is the most common type of congenital methemoglobinemia. It occurs when it’s passed on by both parents, but they don’t have the condition themselves. It affects only the red blood cells. Usually, its only symptom is cyanosis. People with type 1 can have bluish-tinted skin their whole lives without any other symptoms. They may get treated for cosmetic reasons. People with this type have a higher likelihood of developing acquired forms.

Hemoglobin M disease

This type is caused by a genetic mutation that isn’t necessarily inherited from your parents. People with this type don’t have symptoms and don’t need treatment.

Type 2

Type 2 is also known as cytochrome b5 reductase deficiency. It’s the rarest form of methemoglobinemia. Type 2 affects all cells. Only one of your parents needs to pass on the abnormal gene. It can cause severe developmental problems and failure to thrive. Babies born with type 2 usually die in their first year.

This is also known as acute methemoglobinemia. Acquired methemoglobinemia is the most common type of the condition. It’s caused from exposure to certain medicines, chemicals, or foods. People who carry a genetic form of the condition have a higher chance of developing the acquired type. But most people who acquire this condition don’t have a congenital problem. If acquired methemoglobinemia is not treated immediately, it can lead to death.

In babies

Babies are most susceptible to this condition. Babies can develop acquired methemoglobinemia from:

Benzocaine: Benzocaine is found in over-the-counter (OTC) products that may be used to soothe a baby’s sore gums from teething (Anbesol, Baby Orajel and Orajel, Hurricaine, and Orabase). The U.S. Food and Drug Administration recommends that parents and caregivers not use these OTC drugs on children younger than age 2.

Contaminated well water: Infants younger than 6 months may develop acquired methemoglobinemia from contaminated well water that has excess nitrates. Bacteria in a baby’s digestive system mixes with the nitrates and leads to methemoglobinemia. Fully developed digestive systems keep children older than 6 months and adults from developing this nitrate poisoning.

Keep reading: Fertilizer and plant food poisoning »

Solid foods: Certain home-prepared solid foods can have too many nitrates to give to babies before they’re 4 months old. Foods that might have too many nitrates include:

  • beets
  • carrots
  • green beans
  • spinach
  • squash

This is one reason pediatricians tell parents not to give babies solid foods before they’re 4 months old.

In adults

People have developed methemoglobinemia after having medical procedures that used certain topical anesthetics that are often sprayed on to the skin. These include benzocaine, lidocaine, and prilocaine. These may be used to:

Other medicines that have caused this condition are:

  • dapsone (Aczone), which can be used to treat conditions like acne, a type of dermatitis that causes blisters on your arms and buttocks, and a fungal lung infection in people with HIV/AIDS
  • antimalarial drugs

To diagnose methemoglobinemia, your doctor may order tests like:

Methemoglobinemia may be a medical emergency.

The first treatment is infusion with the drug methylene blue. This medication usually helps people quickly. But methylene blue can’t be used on people who have a congenital type of methemoglobinemia.

People who don’t respond to methylene blue may need a blood transfusion.

People with type 1 hereditary methemoglobinemia may receive aspirin therapy.

Learn more: How long does a blood transfusion last? »

Using medications that contain benzocaine when you have one of the following conditions increases your chances of complications from methemoglobinemia:

Some drugs, including dapsone and benzocaine, cause a rebound effect. This means that if you acquired methemoglobinemia from these medicines, it’s possible to be successfully treated with methylene blue and for your methemoglobin levels to increase again 4 to 12 hours later.

Many people who live with type 1 congenital methemoglobinemia don’t have any symptoms. The condition is benign.

There is no effective treatment for people with a congenital form who develop an acquired form. This means that they should not take drugs such as benzocaine and lidocaine.

People who acquire methemoglobinemia from medications can completely recover with proper treatment.

There is no way to prevent genetic types of methemoglobinemia. To prevent acquired methemoglobinemia, try these strategies to avoid the things that can cause it:


Read the label to see if benzocaine is an active ingredient before you buy OTC products. Don’t use products with benzocaine on children under age 2.

Instead of using an OTC product with benzocaine to soothe a teething baby, follow this advice from the American Academy of Pediatrics:

  • Let your child use a teething ring that you’ve chilled in the refrigerator.
  • Rub your baby’s gums with your finger.

Adults shouldn’t use products with benzocaine more than four times a day. Adults also shouldn’t use products with benzocaine if they:

  • have heart disease
  • smoke
  • have asthma, bronchitis, or emphysema

Nitrates in groundwater

Protect wells from contamination by sealing them properly. Also keep wells away from:

  • barnyard runoff, which can contain animal waste and fertilizers
  • septic tanks and sewer systems

Boiling well water is the worst thing to do because it concentrates the nitrates. Softening, filtering, or other ways of purifying water also don’t reduce nitrates.