Mucosal Itch — It’s not the skin, it’s the Internal Itch!

Itching is generally an irritating sensation that results in scratching the affected site. Commonly, itch is associated with infection, allergy, insect bites, or underlying psychiatric conditions, such as anxiety.  

Mucosal itches, on the other hand, refer to itch or irritation that occur in the mucosal linings of the body. Simply put, mucosal areas are the connecting junctions between the external skin and the internal body, such as the vagina, anus, mouth, nose, eyes and ears. We tend to neglect the mucosal areas, yet they play a pivotal role in safeguarding our body against external particles, proteins and even harmful pathogens. 

The understanding of itching over mucosal surfaces is less discussed. We want to increase the awareness about mucosal itching, the possible causes of mucosal itching at different locations, highlight the common causes and encourage appropriate treatment to the respective conditions.

Why does a person experience itch?

Itch is often triggered by a stimulus. The stimulus is picked up by sensory receptors over the affected site. These sensory receptors (known as nociceptors) then activate sensory nerve fibres, which are also known as unmyelinated C-fibres. The nerve fibres will transport the stimulus impulse to the spinal cord and the brain, triggering the perception of ‘itch’ and resulting in a cascade of motor reflexes involving scratching the itch site. Interestingly, both pain and itch share the same sensory fibres, and both symptoms can occur concurrently.

Itch over the Oral Mucosa

The oral mucosa covers the inner cheek (buccal area of the mouth), lips, gums, teeth, the roof of the mouth (known as the palate), the floor of the mouth, tongue and back of the throat. These mucosal regions are highly covered with nerve endings. The maxillary and mandibular nerve from the trigeminal branch supply most regions of the oral mucosa. The back of the oral cavity is also innervated by the vagus nerve.

Common causes of itch over the oral mucosa

• Allergic rhinitis 

Provocation of external allergens in the form of airborne or food particles can trigger the sensory nerve endings in the oral mucosa and result in the unpleasant sensation of itch. Often there can be associated nasal hypersecretion symptoms, watery itchy eyes as well

• Allergy syndrome 

Oral allergy syndrome aka pollen-food allergy syndrome/ latex-fruit allergy syndrome/ dustmites-crustacean allergy

• In oral allergy syndrome, the affected person is sensitized towards inhaled pollen proteins that have similar protein structure in certain food. When the person ingests the food (vegetables/ fruits/ nuts) that have cross-reactive protein as the pollen, an allergic reaction occurs, leading to an immense acute itch in the mouth.

• Similar concept occurs in latex-fruit allergy syndrome, whereby certain fruit such as banana or kiwi, avocado, peach, tomato shares similar structural protein as latex, leading to development of itching or allergy in the mouth following ingesting fruits that have similar protein structure with latex.

• Studies have also shown protein cross reactivity between dustmites and crustaceans, hence one who has dustmites allergy may potentially have oral allergic symptoms to shellfish.

What can I do?

• Able to identify culprit triggering proteins is key in managing oral itch associated with allergy. 

• While history can be useful, allergy tests in the form of blood RAST tests and skin prick tests can also be beneficial in finding the allergens.

• Only by finding out the trigger, one can effectively prevent allergy by avoiding the culprit allergens. 

• Symptomatic relievers in the form of antihistamine and steroid are commonly used to control the allergic symptoms. 

• In the event of anaphylaxis life threatening symptoms, adrenaline and immediate medical care is required to reverse the allergy.

• Thankfully, many of the oral-fruit based allergens can be consumed safely following the heating/cooking process that denatures the allergenic proteins, preventing allergy.

Itch over the Nose, Eye and Ear Mucosa

The nose sensation is supplied by the trigeminal nerve. The ophthalmic nerve supplies the mucous membrane over the eyes, nasal sinuses. The ear mucosal areas are supplied by both the trigeminal nerve and vagus nerve. Similar nerve branches also innervate the oral cavity as discussed previously. This rich network of nerves pick up itch stimuli sending impulses to the spinal cord and brain, resulting in itchy sensation.

Common causes of itch over the nose, eyes and ear mucosa

1. Allergic rhinitis (Rhinoconjunctivitis)

• Itching over the nose, eyes and ear mucosa is associated with rhinitis. The itch receptors on the sensory nerves will activate nerve impulses to the brain and spinal cord following exposure of allergen to the mucosal area. Interestingly, an allergic exposure to the nose can trigger eye/ear symptoms. 

Similarly, an allergic exposure to the eyes or ears can trigger nasal or even oral symptoms, suggesting the interlinking nervous network of these mucosal areas.

What can I do?

• Symptoms can be prevented if triggering allergen(s) is identified and avoided.

• As mentioned, aside from a succinct history, allergy tests can aid diagnosis and pinpointing the allergens.

• Antihistamines, nose sprays, eye drops, saline nasal rinse, steroid medication are frequently used in alleviating and managing the symptoms.

• In allergic rhinitis where there is identifiable allergen(s), immunotherapy can be considered in further managing the allergy.

Itch over Vaginal Mucosa

The mucosal region of the vagina is meant to protect the body from external pathogens and facilitate sexual functions. Itch is a sensation meant to be a warning sign to a person that there is an irritation, inflammation or infection brewing. The clitoris, the pubis, vulva, even the cervix has nerve fibers that can stimulate itch sensation. Change in the surrounding temperature, pH, tissue damage, infections can potentially trigger itch nerve signaling and inflammatory response.

Common causes of itch over vaginal mucosa

• Vaginal infections

Vaginal infection such as yeast (candida) infection can present with vaginal itch. Bacterial STDs such as chlamydia trachomatis, neisseria gonorrhea, trichomonas, mycoplasma genetalium, ureaplasma spp can contribute to vaginal itch.

• Hormonal changes

Hormonal fluctuation, especially lacking in estrogen after menopause can result in itch due to poorer skin and mucosal barrier, and reduced glandular secretion. One may be more predisposed to itch sensation. 

• Vaginal or vulva cancer

Less commonly, yet important not to be missed, itching or pain over the vulva or vaginal area can be due to underlying cancer.

What can I do?

• One should always maintain good vaginal health. Avoid douching, over-cleansing the vulva.

• If there is abnormal vaginal itch and discharge, it is worth seeking medical attention, your doctor may offer vaginal swab tests to evaluate further.

• Regular pap smear should be considered as part of cervical cancer screening/ woman checkup.

• Consider regular STI screening if you are sexually active to pick up and treat vaginal infections early.

• If you are age-eligible, you should consider HPV vaccination if this has not yet been done. 

Itch over Anal Mucosa

The pudendal nerve is the sensory nerve group found over the sacrum/genital region for both male and female that plays an important role in receiving itch stimuli and result in motor reflex of recurring scratching. Itching over the anal mucosal region is more common in male and it affects 5% of the population.

Common causes of itch over anal mucosa

• Anal infection (bacterial, fungal, viral, STDs, parasites and worms)
• Underlying skin inflammatory conditions- eczema or psoriasis
• Structural causes such as haemorrhoids
• Dietary (such as hot and spicy food) and medications
• Underlying medical conditions (untreated diabetes, thyroid disorders etc)

What can I do?

• Take care of your diet and avoid food that can trigger anal itch.

• Maintain skin barrier with comfortable undergarments, avoid friction and irritation to anal region. Avoid douching, perfume, chemical sprays, baby wipes over anal region.

• Topical steroid and antihistamines can be used to alleviate and control itching over the anal region.

• If there is concern of infection or underlying medical conditions, it is important to consult your physician that you are comfortable with for physical examination to evaluate the condition further.

Take home message

Mucosal sites are the ‘guardian’ sites that connect the external skin with the internal body. In view of the nature of the mucosal sites, they are covered with large amounts of complex sensory nerves to pick up any potential threat in the form of inflammation, infection or allergy. 

Itch over the mucosal surfaces behave like alarm bells of the body, signaling potential external danger. Understanding different mucosal itches at different sites and the possible causes aid correct diagnosis and ensure appropriate treatment to be given.

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