A body temperature below 98.6°F is usually normal. That old number, established in the 1800s from armpit readings of 25,000 people, no longer reflects what researchers actually see. A large analysis covering 157 years of temperature data found that average oral temperature has gradually dropped by more than a full degree, landing closer to 97.5°F. A 2023 study of over 35,000 people put the average at 97.9°F. So if your thermometer reads 97-something, you’re likely right in the middle of the modern range.
That said, a consistently low reading can sometimes point to real issues worth understanding. Here’s what might be going on.
Your Thermometer or Timing May Be Off
Before assuming something medical, consider how and when you’re measuring. Forehead thermometers are convenient but less accurate, especially in cold rooms, direct sunlight, or if your skin is sweaty. Ear thermometers can give unreliable readings if there’s earwax buildup or an ear infection. Oral thermometers are more reliable, but drinking cold water or breathing through your mouth right beforehand will pull the number down. For the most consistent results, use the same method each time and wait at least 15 minutes after eating or drinking.
Timing matters too. Your body temperature isn’t fixed. It naturally dips at night as you approach sleep, reaches its lowest point in the early morning hours, then rises before you wake up. There’s also a smaller dip for most people between 2 p.m. and 4 p.m. If you’re checking your temperature first thing in the morning, a reading in the low 97s or even high 96s can be completely expected.
Your Thyroid May Be Underactive
Thyroid hormones directly control your metabolic rate, which is your body’s engine for producing heat. When the thyroid gland doesn’t produce enough of these hormones, a condition called hypothyroidism, your metabolism slows and you generate less warmth. The result is a persistently low body temperature alongside other symptoms like fatigue, weight gain, dry skin, and feeling cold when others around you seem comfortable.
Hypothyroidism is one of the most common medical causes of running cold. It’s especially prevalent in women and becomes more likely with age. A simple blood test can confirm it, and treatment typically brings temperature and energy levels back to normal over a few weeks.
Iron Deficiency Changes How Your Body Makes Heat
Low iron levels interfere with temperature regulation through several pathways at once. Iron-deficient people have trouble maintaining their body temperature in cool environments that don’t bother people with normal iron levels. Research from the National Academies of Sciences found that iron-deficient individuals couldn’t maintain temperature during exposure to cool water (82°F) or cool air (61°F), compared to people with the same body composition and adequate iron.
The reasons stack up. Iron deficiency reduces oxygen delivery to tissues, which limits two key heat-generating responses: constricting blood vessels near the skin to conserve warmth, and ramping up metabolic rate to produce more heat. Beyond the anemia itself, low tissue iron impairs your muscles’ ability to produce energy at the cellular level. Iron deficiency also disrupts the signaling chain between your brain and your thyroid gland, essentially blunting the thyroid’s ability to respond to cold. If you’re running low on temperature and also feeling exhausted, short of breath, or noticing pale skin and brittle nails, iron deficiency is worth checking.
Age Plays a Significant Role
Older adults naturally run cooler, and this isn’t a sign of illness on its own. As you age, body composition shifts: muscle mass decreases, fat distribution changes, and skin and sweat glands work differently. All of these affect thermal regulation. Thyroid function also tends to decline gradually over the decades, reducing heat production. For adults over 65, a baseline temperature in the mid-to-low 97s is common. The practical concern is that this lower baseline makes it harder to detect fevers during illness, since a reading of 99°F might actually represent a significant spike.
Certain Medications Can Lower Temperature
Several common drug classes affect your body’s ability to regulate heat. Beta-blockers, prescribed for high blood pressure and heart conditions, reduce blood flow to the skin’s surface and decrease sweating, both of which affect temperature control. Antipsychotic medications impair sweating and interfere with the brain’s central thermostat. Some antidepressants, including older tricyclic types, also disrupt the sweating mechanism your body uses to regulate its core temperature. If you started a new medication and noticed your readings dropping, the drug could be a factor.
Infections Don’t Always Cause Fever
Most people associate infection with a high temperature, but serious infections can actually push your temperature down. In sepsis, the body’s overwhelming response to an infection, a very low body temperature is a recognized warning sign alongside rapid heart rate, confusion, and difficulty breathing. This is more common in older adults and people with weakened immune systems, whose bodies may not mount the typical fever response. A dropping temperature during an illness you thought was getting better is not something to dismiss.
When a Low Temperature Is an Emergency
A reading below 95°F crosses into hypothermia, which is a medical emergency. Mild hypothermia (90°F to 95°F) causes shivering, confusion, poor judgment, and clumsiness. As the body cools further into moderate hypothermia (around 82°F to 90°F), shivering actually decreases or stops, heart rate slows, and consciousness fades. Severe hypothermia below 82°F can cause breathing to stop entirely.
The most dangerous feature of hypothermia is that the confusion it causes makes people unable to recognize how much trouble they’re in. If someone has stopped shivering but is still cold, that’s a worsening sign, not an improvement. Hypothermia at any stage requires emergency care.
Patterns Matter More Than Single Readings
A one-time reading of 97.2°F after waking up on a cold morning tells you very little. What’s more informative is a pattern. If you consistently read below 97°F at the same time of day using the same thermometer, and especially if you also feel fatigued, cold-intolerant, or foggy, it’s worth investigating. Tracking your temperature at the same time for a week or two gives you and your doctor something concrete to work with. For most people who search this question, the answer is reassuring: 98.6°F was never as universal as we were taught, and your “low” temperature is probably just your normal.