What is this white liquid that comes out of pimples?

White pimples are skin lesions that stand out due to their raised appearance of about 5 mm in diameter. They are located on the surface of the epidermis and contain a purulent liquid of white or yellow color at their center. These small bumps, surrounded by a red halo, are sometimes painful to the touch and can cause scars once the white liquid is drained. Of infectious origin, the pustules are generally papules that have evolved over time. They can be found all over the body, although the face, shoulders, chest, and back are the areas most prone to them.

Several factors contribute to the blockage of hair follicles and thus the emergence of pimples, the most common being excessive sebum production and an increase in keratinocytes, the primary cells of the epidermis. Often, this is accompanied by bacterial proliferation, particularly that of Cutibacterium acnes, a bacterium that feeds on the lipids of sebum and converts them into free fatty acids. These acids create an irritation within the hair follicle. A cascade of immune responses is then triggered, leading to the release of pro-inflammatory cytokines such as interleukins (IL-1 and IL-8).

These inflammatory mediators then attract immune cells, such as neutrophils, to the area of the infected follicle. As a reminder, neutrophils are white blood cells that play a crucial role in defense against bacterial infections. They accumulate around the follicle and phagocytize the bacteria, meaning they internalize them before digesting them. These various inflammatory and infectious mechanisms are the cause of the pus observed in whiteheads.

The white fluid found in some pimples corresponds to pus, a mixture of sebum accumulated in the follicle, neutrophils, dead cells resulting from the initial hyperkeratinization, cellular debris corresponding to fragments of follicular walls, and bacteria.

Why is pus white or yellow?

The white color of pus is primarily due to the massive presence of dead neutrophils. As these cells disintegrate, they release their intracellular content, giving pus an opaque appearance. When the pus is yellowish, it may indicate that plasma proteins, dead cells, and tissue debris are also part of the mix. The color of pus can also depend on the bacteria present. Indeed, some bacteria release pigments or toxins that can alter the color of pus. For example, in the case of infections caused by Pseudomonas aeruginosa, the pus can turn greenish because this bacterium produces pyocyanin, a bluish-colored toxin.

Note : Regular application of antibacterial, anti-inflammatory, and sebostatic treatments, such as benzoyl peroxide, salicylic acid, or sulfur, can help combat pustules. However, if there is no improvement after six to eight weeks of use, or if the pustules multiply, it is advisable to consult a dermatologist.