A lot has been written and published on the Internet about the allergen produced by the cat, Fel D1, which causes an allergic reaction in between 10% and 20% of people. Technically, an allergen is an antigen.
Historically, people generally believed that the Fel D1 allergen is in a domestic cat’s saliva. But it should be said that two studies concluded without doubt that “the most abundant source of Fel D1 allergen is cat skin“, where it ends up after being released from sebaceous glands within the skin as “The amount of Fel d I was significantly higher at the base than the tip of the hair.”
Therefore, the primary source of the Fel D1 allergen is the sebaceous glands of a domestic cat. Their conclusion firstly comes from a study, “Fel D1 allergen: skin or saliva?” It was published in 1992.
Sebaceous glands are part of the cat’s scent marking system and are dotted around the body as indicated in the image below:
An earlier study published the year before, came to the same conclusion. This earlier study is titled, “Fel D1 allergen distribution in cat fur and skin”. In this study they used a technique called immunohistochemical staining procedures to detect the Fel D1 allergen on fur and skin. They also used skin biopsy specimens to detect how much Fel D1 was on the skin.
The objective of the study as you can guess was to find out where the Fel D1 antigen was located in cat fur and skin samples and analyse the concentration in the fur.
The researchers used 11 different cats and 100 strands of fur. They used 24 skin biopsy specimens taken from shaved areas. I presume these were living cats under test conditions which I don’t like by the way.
They removed the hair strands to analyse them using the immunohistochemical technique mentioned.
They found that “concentrations of [the Fel D1 antigen] were 10 times higher at the root of the hair strand compared to the tip. This difference was attributed to variations in the thickness of the hair cortex.”
And they found that the antigen accumulated on the surface of the hair strand. It can also penetrate into the hair strand and therefore Fel D1 can be found inside the hair as well as on it.
They found the Fel D1 antigen at various locations on and in the skin including epithelial squamous cells, within the epidermis, hair follicles, on the surface of the epidermis and in sebaceous gland cells.
The antigen was mainly stored on the surface of the epidermis (skin) and on fur.
When you note the findings of this study with the later one the overall conclusion is that the cat allergen which causes an allergic reaction in people is mainly on the skin and fur coming from the sebaceous glands and also to a lesser extent from the saliva of the cat when they groom themselves.
For the sake of completeness, it is my supposition that the antigen ends up in dried saliva on the cat’s fur after they’ve groomed themselves and licked it up from the fur and skin. The saliva is then deposited on the fur with the antigen in their saliva.
It then flies off the fur and floats round the room to end up being deposited on household items such as furniture. That’s why people who are allergic to cats can feel that reaction in one room when the cat is in another or another part of the house.
