Cedar fever explained

Cedar fever is a common central Texas allergy: an allergic reaction to the pollen of mountain cedar trees, not a flu or a virus.¹ Mountain cedar releases its pollen in winter, from early December to early February.³ The Texas A&M Forest Service notes that its pollination period falls in the middle of cold and flu season.²

Where mountain cedar grows

Mountain cedar is a juniper: the name is one of the common names of Ashe juniper, Juniperus ashei, which also goes by rock cedar, post cedar and Texas cedar.⁴ The Texas A&M Forest Service says Ashe juniper is the predominant species of mountain cedar in Texas.¹

The main population grows in west-central Texas, largely on the Edwards Plateau, and separate populations grow in southwestern Missouri and Arkansas, in the Arbuckle Mountains of southern Oklahoma, and in Coahuila, Mexico.⁴ The trees usually grow on shallow soils formed from limestone and rarely reach more than 30 feet tall.⁴ Over the last century, Ashe juniper has spread into neighboring grasslands, which the Fire Effects Information System ties to fire suppression and poor rangeland management.⁴

The Texas A&M Forest Service says cedar fever is worst west of I-35, where juniper grows mixed in with oaks.¹

When the pollen flies

Only male juniper trees release pollen; female trees carry berry-like cones instead.² The Texas A&M Forest Service describes the season a little differently from the early December to early February span above: it says the trees typically begin producing pollen in mid-December, reach a peak in mid-January and then taper off slowly toward the beginning of March.²

Colder weather sets the trees off.¹ The Forest Service says their favorite time to release pollen is right after a cold front, when the air dries out, the wind picks up and the air pressure shifts.¹ Every pollen cone on a tree can open at one time, and the trees can look as if smoke is coming off them.¹ There are millions of junipers releasing pollen at the same time, which puts a higher concentration of pollen in the air.²

On AllergyNest, each metro page, including those for Austin, San Antonio and Waco, lists juniper among the day’s plants whenever Google reports it for that metro, and how our index works explains what that level can and can’t tell you.

Why the pollen travels so far

Several factors contribute to the long-distance transport of mountain cedar pollen.³ The grains are small, about 19 to 22 micrometers across, and light.³ Strong temperature and pressure gradients also play a part, and relative humidity below 50% helps the pollen release and travel.³ Weather in the southern Great Plains is dominated by dry, cold air moving in from the Rocky Mountains and the Canadian Arctic, and when it collides with warmer, more humid air from the southeast, the resulting instability can carry tiny particles over long distances.³

The distances can be large: genetic testing identified mountain cedar pollen in January air samples from London, Ontario, and air-flow models traced its path back to Texas and Oklahoma.³ The same paper cites an earlier study that found pollen in London, Ontario, likely came from the Edwards Plateau region near Austin, Texas, about 2,400 kilometers, or roughly 1,500 miles, away.³ Earlier molecular work by the same research group confirmed mountain cedar pollen in air samples from Tulsa, Oklahoma, on 11 days in December 2013 and January 2014.³

What cedar fever feels like

Tree pollen allergy causes seasonal allergic rhinitis, also called hay fever.⁶ The Texas A&M Forest Service lists fatigue, sore throat, runny nose, partial loss of smell, itchy, watery eyes, blocked nasal passages and sneezing among cedar fever’s symptoms.¹ AAFA’s list of hay fever symptoms on its tree pollen page also includes postnasal drip, an itchy nose, eyes, ears and mouth, swelling around the eyes, and shortness of breath, coughing or wheezing.⁶

Sources disagree on whether cedar fever brings an actual fever. AAFA says that even though “fever” is in the name, cedar fever is not a contagious illness or a virus that causes a fever.⁶ ACAAI says that hay fever in general, despite the name, does not cause a fever.⁷ The Texas A&M Forest Service puts it differently: it says some people with cedar fever do run a fever, but that cedar pollen will rarely push body temperature above 101.5°F.¹ If a fever runs higher than that, it says, pollen likely isn’t the cause.¹

Because mountain cedar pollinates in the middle of cold and flu season, it is not uncommon for people with cedar fever to mistake their symptoms for a cold or the seasonal flu.² A Forest Service biologist points to mucus as a clue: if it runs clear, he says, it’s an allergy, and if it has color, it’s probably a cold or the flu.¹

Who gets cedar fever

AAFA says that in Arizona, Missouri, New Mexico, Oklahoma and Texas, cedar fever is most common from December through February.⁶ The Texas A&M Forest Service says the pollen can be so concentrated that it may affect even people who aren’t generally susceptible to allergies.¹

Sources also differ on how allergenic the pollen itself is. A study in PLOS ONE calls mountain cedar pollen highly allergenic and the major cause of hay fever in Texas.³ It describes Ashe juniper as the most allergenic species of the cypress family in North America, considered equal to ragweed in its potential to cause allergy.³ The Texas A&M Forest Service, by contrast, says the pollen isn’t particularly allergenic or harmful, but is so concentrated that it overwhelms the immune system.¹ Our juniper and cedar page covers the tree and its cypress-family relatives in more detail.

Eastern redcedar later in the season

Eastern redcedar, Juniperus virginiana, is a different juniper, native to the eastern United States and Canada.⁵ Its pollen is spread by the wind, and it pollinates from February in the south and east to May in the north and west.⁵

The two seasons can overlap: in more eastern parts of Texas, eastern redcedars pollinate around the same time as mountain cedar, between December and January.¹ In Tulsa, Oklahoma, eastern redcedar’s season begins in February and continues through April.³ In archived air samples from several sites in Texas, more than 99% of the cypress-family pollen in late January was mountain cedar, while the February samples held only eastern redcedar pollen.³ In Texas, the Forest Service notes, mountain cedar tapers off toward the beginning of March, just as oak pollen and other spring allergens start.²

When to see an allergist

AAFA says cedar fever is diagnosed the same way as other tree pollen allergies, and it suggests asking for a referral to a board-certified allergist if symptoms do not improve.⁶ It says an allergist can diagnose a tree pollen allergy by asking about a person’s history, doing a physical exam and running tests to find which trees they are allergic to.⁶ Through testing, ACAAI says, an allergist can pinpoint which pollens bring on symptoms.⁸ For questions about managing cedar fever, talk to an allergist.