The burning and painful sensations
associated with capsaicin result from its chemical interaction with sensory
neurons. Capsaicin, as a member of the vanilloid family, binds to a receptor
called the vanilloid receptor subtype 1 (TRPV1). First cloned in 1997, TRPV1 is
an ion channel-type receptor. TRPV1, which can also be stimulated with heat,
protons and physical abrasion, permits cations to pass through the cell
membrane when activated. The resulting depolarization of the neuron stimulates
it to signal the brain. By binding to the TRPV1 receptor, the capsaicin
molecule produces similar sensations to those of excessive heat or abrasive
damage, explaining why the spiciness of capsaicin is described as a burning
sensation.
Early research showed capsaicin to evoke a
long-onset current in comparison to other chemical agonists, suggesting the
involvement of a significant rate-limiting factor. Subsequent to this, the
TRPV1 ion channel has been shown to be a member of the superfamily of TRP ion
channels, and as such is now referred to as TRPV1. There are a number of
different TRP ion channels that have been shown to be sensitive to different
ranges of temperature and probably are responsible for our range of temperature
sensation. Thus, capsaicin does not actually cause a chemical burn, or indeed
any direct tissue damage at all, when chili peppers are the source of exposure.
The inflammation resulting from exposure to capsaicin is believed to be the
result of the body's reaction to nerve excitement. For example, the mode of
action of capsaicin in inducing bronchoconstriction is thought to involve
stimulation of C fibers culminating in the release of neuropeptides. In
essence, the body inflames tissues as if it has undergone a burn or abrasion
and the resulting inflammation can cause tissue damage in cases of extreme
exposure, as is the case for many substances that cause the body to trigger an
inflammatory response.
Acute Health Effects
Capsaicin is a strong irritant requiring
proper protective goggles, respirators, and proper hazardous material-handling
procedures. Capsaicin takes effect upon skin contact (irritant, sensitizer),
eye contact (irritant), ingestion, and inhalation (lung irritant, lung
sensitizer). LD50 in mice is 47.2 mg/kg.
Painful exposures to capsaicin-containing
peppers are among the most common plant-related exposures presented to poison
centers. They cause burning or stinging pain to the skin and, if ingested in
large amounts by adults or small amounts by children, can produce nausea,
vomiting, abdominal pain, and burning diarrhea. Eye exposure produces intense
tearing, pain, conjunctivitis, and blepharospasm.
When used for weight loss in capsules,
there has been a report of heart attack; this was thought to be due to excess
sympathetic output.
Treatment After Exposure
The primary treatment is removal from
exposure. Contaminated clothing should be removed and placed in airtight bags
to prevent secondary exposure.
For external exposure, bathing the mucous
membrane surfaces that have contacted capsaicin with oily compounds such as
vegetable oil, paraffin oil, petroleum jelly (Vaseline), creams, or
polyethylene glycol is the most effective way to attenuate the associated
discomfort;[citation needed] since oil and capsaicin are both hydrophobic
hydrocarbons the capsaicin that has not already been absorbed into tissues will
be picked up into solution and easily removed. Capsaicin can also be washed off
the skin using soap, shampoo, or other detergents. Plain water is ineffective
at removing capsaicin, as are bleach, sodium met bisulfite and topical antacid
suspensions.[citation needed] Capsaicin is soluble in alcohol, which can be
used to clean contaminated items.
When capsaicin is ingested, cold milk is
an effective way to relieve the burning sensation (due to caseins having a detergent
effect on capsaicin; and room-temperature sugar solution (10%) at 20 °C (68 °F)
is almost as effective. The burning sensation will slowly fade away over
several hours if no actions are taken.
Capsaicin-induced asthma might be treated
with oral antihistamines or corticosteroids.
Effects on Weight Loss and Regain
There is no evidence showing that weight loss is directly correlated
with ingesting capsaicin. Well-designed clinical studies have not been
performed because the pungency of capsaicin in prescribed doses under research
prevents subject compliance.
