Linoleic acid is a vital component in normal sebum that does what it is supposed to: Protect the skin.

Your skin isn't a dead leather outer wrapping and your sebum isn't a layer of dead grease. Both are composed of active living cells that perform many vital functions.  Soaps, cleansers and topicals prevent them from functioning. 

Linoleic acid is a vital component in normal sebum that does what it is supposed to: Protect the skin.  

 Skin and sebum in people (and other animals) prone to acne and other skin problems have been found to be deficient in linoleic Acid. Sebum deficient in linoleic acid is hard and sticky and clogs pores. It looks greasy and has fewer protective and anti-inflammatory properties.

Key points:

• Acne and other problem prone skin (in people and animals) are lacking in linoleic acid.
  Linoleic acid is a component in the ceramides that make skin strong and impermeable and thus less easily ruptured and less sensitive to irritations.
• This deficiency can be changed with topical application.
• Grape seed and Safflower oil are over 70% linoleic acid.
• Linoleic Acid inhibits the enzymes that convert Testosterone to DHT. Both types. So it can help with hirsutism, hairloss and acne.
• Linoleic Acid is anti-inflammatory and protects the skin from UV damage.
• Linoleic Acid inhibits melatonin and thus fades hyperpigmentation.
• Linoleic acid is anti-microbial, as in anti P. Acnes blamed for acne formation.
• Linoleic acid deficiency causes an increase in interluekin -1a which is a factor inflammatory response.
• Tretinoin (Retin A & the like) alters the lipid profile improving the linoleic acid composition.
• Linoleic Acid improves the peroxisome proliferator-activated receptors (PPAR) and retinoid X receptor (RXR) situation that regulates sebum production and hyperkeritinization/differenciation (and is what accutane affects)
• Increase formation of Lamellar granules that produce the enzymes involved in normal exfoliation. They also form the armor that makes your skin strong. Acne prone skin has been found to contain fewer lamellar granules.
• Thyroid hormones affects your lipid profile. One way that perhaps both hypo and hyperthyroid conditions affect acne.
• We don't necessarily have a dietary or systemic deficiency in linoleic acid. Just in the sebum and thus a topical application is the best course of action. This tendency is genetic.

Examples of skin problems affected by a deficiency in linoleic acid include acne, eczema, psoriasis, keratosis pilares, hypersensitivity to allergens, and dry itchy sensitive skin of all types--aka dermatitis. This applies to all mammals, such as your itchy pet dog.