'Waking up and not being able to smell," said Christine Kelly, "you feel like you're separated from your loved ones - your environment - by a glass bubble. You're tapping on it, but no one can hear you."

It was 2012, and she was recovering from a weeklong sinus infection that damaged the delicate olfactory tissues in her nose. She was devastated.

"I always remember," she said, "that was the last day I had a sense of smell." She later learned the name for her condition: anosmia.

Kelly, who lives in England, was in Philadelphia recently to lead a session on "smell training" - working with specific odors to retrain the brain and olfactory receptors to recognize scents.

Anosmia (pronounced an-OZ-me-uh) is an "invisible" disorder, and also may be hidden by patients who are embarrassed or may not realize what they're missing. They develop the condition after colds and sinus infections, chemical exposure, or brain injury that severs the olfactory nerve; congenital anosmia is rare. About 2 percent of North Americans report problems with their sense of smell, according to the National Institute on Deafness and Other Communication Disorders.

The chemical familiarity of family, the aromas of food and nature are all gone, along with the unpleasant odors of natural gas and rotting food, which are normally read as warning signs.

Many anosmics become depressed. Kelly, who is 57 and resides in Chilbolton, Hampshire, plunged into learning about the condition. Training has helped, to a degree: "My broken keyboard has a few more keys." Whether the training is responsible, however, has not been proved.

About 18 people showed up for her 21/2-hour workshop at the Monell Chemical Senses Center, the West Philadelphia institution devoted to the science of taste and smell.

Kelly, a lay advocate who was trained as an archaeologist, talked about the condition and then had participants sample various sodas. They shared their experiences in small groups before going on to teas, and then relying on smell alone for essential oils.

Although smell is intimately related to taste, anosmics can distinguish among the five basics (sweetness, sourness, saltiness, bitterness, and umami - a meaty, savory smell). Within those categories, however, flavor distinctions can be diminished or disappear. (Try holding your nose and tasting something.)

"I used to love coffee; now it tastes like dust," said Sharon Fogarty, 55, a performing artist from New York. "And a really good wine . . . rusty nails with dry leaves."

Fogarty lost her sense of smell and taste after fainting at a restaurant and fracturing the side of her skull. Focusing hard can sometimes help but often not.

"I don't think I smelled the juniper," she said after after sniffing essential oils at the workshop. The four bottles in front of her, "I can't tell apart."

After her accident four years ago, she said, "there was an anxiety that I couldn't pinpoint." She recalled feeling that "everything is new. I can't smell what's familiar. There was a loss of trust."

Like Kelly, she was suddenly shut off from the world she knew.

When Fogarty told her physician that she couldn't smell or taste, he said, "Oh, yeah, that happens. It's not coming back." She said her ear, nose, and throat doctor said he'd never had anyone recover his or her sense of smell after severing an olfactory nerve. But she paid $20 for the Monell workshop because, she said, "sometimes I think I can smell something."

Perhaps she could build on it.

Smell training is a basic method of olfactory rehabilitation developed in recent years by Thomas Hummel, the lead researcher at the Smell and Taste Clinic at Dresden University Medical School in Germany.

It involves smelling four essential oils - rose, eucalyptus, lemon, and clove were originally recommended – twice a day for a few minutes. But adding different odors - as well as objects like rubber bands and crayons - to the aroma arsenal may help awaken the brain, Kelly said. The key is to focus on the smells; don't try to read emails at the same time.

Keep training, and track your progress.

"It's active, not passive," Kelly said. "You're asking your brain to do something that is really hard. You can't learn to play the piano in five minutes."

She posts guidance at www.smelltraining.co.uk.

Does it work?

It seems to for some people, said Monell researcher Beverly Cowart, an expert on olfactory disorders. But "it doesn't work for everybody, and we're still sorting out why," she said.

Other researchers, noting that there is no "gold standard" treatment for loss of smell, concluded in a March review of 10 olfactory training studies that the evidence suggests the process works, although the mechanism is unclear and success may depend on the cause of the problem.

Still, research on anosmia has been limited.

"People don't talk about it very much," Cowart said. "When we had an active clinic, patients would often say, 'I didn't know this could happen to anybody.' " She said most large studies have focused on aging. "You have a lot of older people with smell loss, but they're often not aware of it because it happens so gradually."

Sarita Mungo, 52, suffered a serious sinus infection two years ago. Her doctor prescribed prednisone and an inhaler. Her sinuses recovered, but she gradually lost her sense of smell and taste. It was so gradual that she waited eight months to see her family physician, and he said there was nothing she could do.

Mungo sought a second opinion, and that doctor recommended the smell training. Still, she was skeptical.

"I thought it wouldn't work," she said. But she then started accepting the situation, and arrived at the Monell training with a more open mind.

Perhaps, she said, "it doesn't have to be as bad as it is."