It can take 75,000 saffron blossoms to produce a single pound of saffron spice. Saffron is primarily cultivated and harvested by hand and forty hours of labor are needed to pick 150,000 flowers. Due to the amount of work required for harvest, saffron is considered one of the world's most expensive spices. In 2013, 0.06 ounces of saffron could be purchased for $16.26 or the equivalent of $4,336 per pound (retail) or as little as about $2,000 per pound wholesale. A pound of saffron contains between 70,000 and 200,000 threads. To increase profits saffron is frequently adulterated with cheaper flowers such as marigold and safflower or dyed. The risk of contaminated or dyed counterfeit herbs used to replicate saffron is high so exercise caution when choosing a supplier. It can be dangerous to use adulterated saffron topically as this could trigger allergic reactions or cause undesired changes to the skin.
 
Saffron contains more than 150 volatile and aroma-yielding compounds mainly terpenes, terpene alcohol and their esters. Saffron's taste and hay-like fragrance result from the chemicals picrocrocin and safranal. Safranal is an aromatic aldehyde, which is the main component of saffron’s volatile plant oil. Saffron also contains a carotenoid pigment, crocin, which imparts a rich golden-yellow hue to dishes and textiles. High concentrations of saffron in skin care formulations can stain the skin. Its recorded history dates to 7th-century BC, and it has been traded and used for over four millennia. 90% of the world production of saffron comes from Iran.
 
One strategy for cancer prevention today is chemoprevention using readily available natural substances from vegetables, fruits, herbs and spices. Saffron (Crocus sativus), a member of the family Iridaceae, has drawn attention because apart from its use as a flavoring agent, pharmacological studies have demonstrated many health-promoting properties including free-radical scavenging, anti-mutagenic and immuno-modulating effects.
 
Saffron contains minerals like copper, potassium, calcium, manganese, iron, selenium, zinc and magnesium. Additionally, vitamin A, folic acid, riboflavin, niacin and vitamin C make saffron useful for dry or mature skin care products. Because of its hydrating properties, it is beneficial in hydrating creams and heavy moisturizers, scrubs and facial masks. 
 
One important biological activity of saffron for cosmetics formulators, and the most mentioned activity in most studies, is its anti-inflammatory effects. The observed anti-inflammatory properties have suggested that saffron and its phytochemicals enhance antioxidant enzymes as well as the scavenging of reactive oxygen species which are key mediators in the promotion of oxidative stress and subsequent inflammatory response. 
Two clinical trials on saffron as an antipruritic and complexion promoter in skin care confirmed that saffron was more efficient than the placebo. The anti-inflammatory effects of the extracts may be due to their content of flavonoids, tannins, anthocyanins, alkaloids and saponins. In chronic inflammation, both water-based and ethanol-based stigma extracts, as well as ethanol-based petal extract, showed anti-inflammatory effects; however, water-based petal extract exhibited no significant anti-inflammatory activity. 
 
Findings of in-vivo studies have revealed that saffron has negligible toxicity. Daily consumption of saffron at up to 1.5 g/day has not shown any adverse effect. However, doses over 5 g are toxic, and at 20 g are lethal. Saffron doses over 10 g have been associated with spontaneous abortion, making its internal use contraindicated for those who are pregnant.
 
Methods of incorporating saffron into skincare formulations may include using the whole or powdered dried herb, infusions or tinctures of the herb or saffron essential oil, absolute and resinoid. While saffron does have GRAS (Generally Recognized As Safe) status, IFRA (International Fragrance Association) recommends that safranal should not be used at concentrations over 0.005% in skin-contact cosmetic formulations because it is a known skin sensitizer.
 
References:
 

1. N Aktar, HMS Khan, S Ashraf, IS Mohammad, A Ali. Skin depigmentation activity of Crocus sativus extract cream. Tropical Journal of Pharmaceutical Research. 2014. Vol 13, No 11.
2. Moshiri M, Vahabzadeh M, Hosseinzadeh H. Clinical Applications of Saffron (Crocus sativus) And its Constituents: A Review. Drug Res (Stuttg). 2015Jun;65(6):287-95. doi: 10.1055/s-0034-1375681. Epub 2014 May 21. Review. PubMedPMID: 24848002.
3. Gardner, Z., McGuffin, M. American Herbal Products Association’s Botanical Safety Handbook, Second Edition. 2013. pp 280-283.
4. A Survey on Saffron in Major Islamic Traditional Medicine ... (n.d.). Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3637900/
5. Verma, R. S.; Middha, D. (2010), "Analysis of Saffron (Crocus sativus L. Stigma) Components by LC–MS–MS", Chromatographia, 71 (1–2), pp. 117–123, doi:10.1365/s10337-009-1398-z
6. Tisserand, R., Young, R. Essential Oil Safety: A Guide for Health Care Professionals. 2013. p 412.