Body Asymmetry: Why Is One Hand or Breast Bigger?

Breast or hand asymmetry (one is larger than the other) is not unusual in the human form. For example, an Australian study of 584 healthy females found a common right-sided bias in how long or strong bones were in the upper extremities (arms).

In most cases, asymmetry is no threat to health though some people may want to correct a visible concern, like having plastic surgery for uneven breasts. A change can mean an underlying health issue, though, such as breast cancer or even a genetic condition.

This article explains some of the reasons why body asymmetry can occur, and why you may want to talk about your body shape with a healthcare provider to determine what care, if any, is needed.

Why Is One Breast Bigger Than the Other?

Breast asymmetry occurs in many people. It’s common for individual breasts to be of different volumes or different shapes.

Asymmetric breasts are most commonly a normal finding—especially among young females where malignancy is rare—but there are aesthetic treatment options. Surgery is generally considered best for adult females, since asymmetry may go away on its own as breast development is completed, although surgery to correct breast asymmetry in adolescents has been studied.

Surgical options to correct for breast asymmetry include breast lift, breast reduction, and breast augmentation. With lipofilling procedures, fat taken from a woman’s own body, or autologous fat, is harvested, processed, and grafted to the breast.

Although uneven breasts are a common and normal finding, there has been some research done that links asymmetric breasts and breast cancer risk. However, such associations need to be supported by further study.

Hemihypertrophy: Why Is One Hand Bigger Than the Other?

Hemihypertrophy means that one side of the body has grown more than the other. For example, some people have different-sized hands, with one hand being larger than the other.

Genetic causes are at work in some cases of asymmetry caused by hemihypertrophy. They include:

• Beckwith-Wiedemman syndrome
• Proteus syndrome
• Neurofibromatosis type 1

These syndromes are complicated and managed by pediatricians, geneticists, and orthopedic surgeons. Importantly, the presence of associated tumors must be ruled out.

Intrauterine Growth Retardation and Developmental Instability

Intrauterine growth restriction (IUGR) affects up to 10% of pregnancies in the general population, usually emerging after 32 weeks of gestation. It is not the same as being small for gestational age (SGA) but otherwise healthy. IUGR can often increase the risk of some health problems for the baby.

IUGR can be defined as either symmetric or asymmetric. Asymmetric IUGR is usually due to placental insufficiency, with impaired blood flow, which means a fetus isn’t receiving adequate oxygen and nutrition via the placenta. This impaired placental blood flow can be due to many things, including:

• Smoking
• Alcohol and drug use
• Underlying health issues, including high blood pressure or heart disease
• Nutrition challenges
• Living at a high altitude
• Pregnancy complications

Blood flow to a fetus with asymmetric IUGR is directed to vital organs and head circumference is maintained. However, the abdominal circumference is decreased due to a smaller liver size, limbs are scrawny, and the skin is thin because there’s less fat. At birth, limbs with reduced muscle mass can appear asymmetric. In severe cases, even vital organ growth is stunted.

In other words, if the uterine environment is off by even a little, it’s possible that this disturbance, or developmental instability, may result in slight discrepancies in hand, foot, and breast size.

Summary

Many people find that the hands, feet, legs, or breasts on one side of the body are not the same size on the other side of the body. This is called asymmetry and is quite common; about 25% of adult females, for example, have asymmetrical breasts.

There are a number of possible causes for asymmetry, most of them benign. In rare cases, the difference in size and shape can be due to a health condition. Your healthcare provider can diagnose the reason for asymmetry and discuss any necessary treatment options with you.