What is this white liquid that comes out of spots?

White spots are skin lesions that stand out due to their raised appearance of approximately 5 mm in diameter. They are located on the surface of the epidermis and contain a purulent liquid of white or yellow colour at their centre. These small bumps, surrounded by a red halo, are sometimes painful to touch and can cause scars once the white liquid is drained. Infectious in 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 spots, the most common being excessive sebum production and an increase in keratinocytes, the primary cells of the epidermis. This is often 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 subsequently 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 defending against bacterial infections. They accumulate around the follicle and phagocytose the bacteria, meaning they internalise them before digesting. These various inflammatory and infectious mechanisms are the cause of the pus observed in whiteheads.

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

Why is pus white or yellow?

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

Note : Regular application of antibacterial, anti-inflammatory, and sebostatic treatments, such as benzoyl peroxide, salicylic acid, or sulphur, 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.